<PAGE>   1

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                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                            ------------------------

                                   FORM 8-K/A

                            ------------------------

                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(D) OF THE
                        SECURITIES EXCHANGE ACT OF 1934

                                OCTOBER 1, 1999
                DATE OF REPORT (DATE OF EARLIEST EVENT REPORTED)

                              CSK AUTO CORPORATION
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                    DELAWARE
                 (STATE OR OTHER JURISDICTION OF INCORPORATION)

<TABLE>
<S>                                            <C>
                  001-13927                                     86-0765798
          (COMMISSION FILE NUMBER)                   (IRS EMPLOYER IDENTIFICATION NO.)

           645 E. MISSOURI AVENUE,                                 85012
         SUITE 400, PHOENIX, ARIZONA                            (ZIP CODE)
  (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)
</TABLE>

                                 (602) 265-9200
              (REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE)

                                      N/A
         (FORMER NAME OR FORMER ADDRESS, IF CHANGED SINCE LAST REPORT)

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>   2

ITEM 2.  ACQUISITION OR DISPOSITION OF ASSETS

     On October 15, 1999, the Registrant filed a current report on Form 8-K and
reported under Item 2 that on October 1, 1999, the Registrant, through its
wholly-owned subsidiary, CSK Auto, Inc., acquired from PACCAR Inc all of the
outstanding capital stock of Al's and Grand Auto Supply, Inc., formerly known as
PACCAR Automotive, Inc., a retailer of automotive parts and accessories. Because
it was impracticable to provide the required financial statements for the
acquired business and pro forma financial information related to the transaction
at the time of the filing, such financial statements and pro forma financial
information were not included with that report on Form 8-K. Item 7 herein
supplements the earlier filing by providing the required financial statements
and the pro forma financial information.

ITEM 7.  FINANCIAL STATEMENTS AND EXHIBITS

     (a) Financial statements of business acquired.

     The following financial statements for PACCAR Automotive, Inc. and
subsidiary are listed below and made a part hereof:

        AUDITED FINANCIAL STATEMENTS

        Report of Independent Auditors

        Consolidated Balance Sheet as of December 25, 1998

        Consolidated Statement of Income for the year ended December 25, 1998

        Consolidated Statement of Stockholder's Equity for the year ended
         December 25, 1998

        Consolidated Statement of Cash Flows for the year ended December 25,
         1998

        Notes to Consolidated Financial Statements

        UNAUDITED INTERIM FINANCIAL STATEMENTS

        Condensed Consolidated Balance Sheet as of September 25, 1999
(unaudited)

        Condensed Consolidated Statement of Income (Loss) for the nine months
         ended September 25, 1999 and September 25, 1998 (unaudited)

        Condensed Consolidated Statement of Cash Flows for the nine months ended
         September 25, 1999 and September 25, 1998 (unaudited)

        Notes to Condensed Consolidated Financial Statements (unaudited)

     (b) Pro forma financial statements.

     The following unaudited pro forma financial statements for CSK Auto
Corporation and subsidiary are listed below and made a part hereof:

        Pro Forma Condensed Consolidated Income Statement for the year ended
         January 31, 1999 (fiscal 1998) (Unaudited)

        Pro Forma Condensed Consolidated Income Statement for nine months ended
         October 31, 1999 (Unaudited)

        Notes to Pro Forma Condensed Consolidated Financial Statements
(Unaudited)

                                        1
<PAGE>   3

     (c) Exhibits

<TABLE>
<C>    <S>
 2.1*  Stock Purchase Agreement between CSK Auto Inc, an Arizona
       corporation, and PACCAR Inc, a Delaware corporation, dated
       as of August 20, 1999.

 4.1*  Third Amended and Restated Credit Agreement, dated as of
       September 30, 1999, among CSK Auto, Inc., The Chase
       Manhattan Bank, DLJ Capital Funding, Inc., Lehman Commercial
       Paper Inc. and the lenders from time to time parties
       thereto.

 23.1  Consent of Ernst & Young LLP
</TABLE>

---------------
* Previously filed

                                        2
<PAGE>   4

               REPORT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

The Board of Directors and Stockholder
PACCAR Automotive, Inc.

     We have audited the accompanying consolidated balance sheet of PACCAR
Automotive, Inc. and subsidiary (the Company) as of December 25, 1998, and the
related consolidated statements of income, stockholder's equity, and cash flows
for the year then ended. These financial statements are the responsibility of
the Company's management. Our responsibility is to express an opinion on these
financial statements based on our audit.

     We conducted our audit in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.
We believe that our audit provides a reasonable basis for our opinion.

     In our opinion, the financial statements referred to above present fairly,
in all material respects, the consolidated financial position of PACCAR
Automotive, Inc. and subsidiary at December 25, 1998, and the consolidated
results of their operations and their cash flows for the year then ended, in
conformity with generally accepted accounting principles.

                                          ERNST & YOUNG LLP

Seattle, Washington
November 15, 1999

                                        3
<PAGE>   5

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

                           CONSOLIDATED BALANCE SHEET
                               DECEMBER 25, 1998

<TABLE>
<CAPTION>
                                                                (IN THOUSANDS)
                                                                --------------
<S>                                                             <C>
ASSETS
Current assets:
  Cash......................................................       $    348
  Accounts receivable, net of allowance of $474.............          3,606
  Inventories...............................................         77,708
  Prepaid expenses and other current assets.................          2,167
  Deferred income taxes.....................................          1,421
                                                                   --------
Total current assets........................................         85,250
Property and equipment, net.................................         46,420
Deferred income taxes.......................................            442
Goodwill and other assets, net..............................         11,541
                                                                   --------
          Total assets......................................       $143,653
                                                                   ========
LIABILITIES AND STOCKHOLDER'S EQUITY
Current liabilities:
  Accounts payable..........................................       $ 34,413
  Accrued payroll and related expenses......................          3,323
  Other.....................................................          3,495
                                                                   --------
Total current liabilities...................................         41,231
Capital lease obligation....................................          4,586
Due to PACCAR Inc...........................................         50,577
Other noncurrent liabilities................................         10,990
Stockholder's equity:
  Common stock, $0.01 par value:
  Authorized shares -- 50,000
  Issued and outstanding shares -- 1,000....................         49,822
Additional paid-in capital..................................         20,073
Accumulated deficit.........................................        (33,626)
                                                                   --------
Total stockholder's equity..................................         36,269
                                                                   --------
Total liabilities and stockholder's equity..................       $143,653
                                                                   ========
</TABLE>

                            See accompanying notes.

                                        4
<PAGE>   6

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

                        CONSOLIDATED STATEMENT OF INCOME
                          YEAR ENDED DECEMBER 25, 1998

<TABLE>
<CAPTION>
                                                                (IN THOUSANDS)
                                                                --------------
<S>                                                             <C>
Net sales...................................................       $212,050
Cost of sales...............................................        118,726
                                                                   --------
Gross profit................................................         93,324
Store direct expenses.......................................         59,271
Warehouse and distribution expenses.........................         11,172
General and administrative expenses.........................         16,324
                                                                   --------
Operating profit............................................          6,557
Other income................................................            432
                                                                   --------
Income before income taxes..................................          6,989
Income taxes................................................          2,972
                                                                   --------
Net income..................................................       $  4,017
                                                                   ========
</TABLE>

                            See accompanying notes.

                                        5
<PAGE>   7

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

                 CONSOLIDATED STATEMENT OF STOCKHOLDER'S EQUITY

<TABLE>
<CAPTION>
                                                       COMMON STOCK       ADDITIONAL
                                                     -----------------     PAID-IN      ACCUMULATED
                                                     SHARES    AMOUNT      CAPITAL        DEFICIT
                                                     ------    -------    ----------    -----------
                                                                          (IN THOUSANDS)
<S>                                                  <C>       <C>        <C>           <C>
Balance at December 26, 1997.......................  1,000     $49,822     $16,399       $(34,278)
Dividend paid......................................     --          --          --         (3,365)
  Capital contribution from PACCAR Inc.............     --          --       3,674             --
  Net income.......................................     --          --          --          4,017
Balance at December 25, 1998.......................  1,000     $49,822     $20,073       $(33,626)
                                                     =====     =======     =======       ========
</TABLE>

                            See accompanying notes.

                                        6
<PAGE>   8

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

                      CONSOLIDATED STATEMENT OF CASH FLOWS
                          YEAR ENDED DECEMBER 25, 1998

<TABLE>
<CAPTION>
                                                              (IN THOUSANDS)
                                                              --------------
<S>                                                           <C>
OPERATING ACTIVITIES
Net income..................................................     $  4,017
Items included in net income not affecting cash:
  Depreciation and amortization.............................        4,901
  Loss on sales of property and equipment...................          119
  Change in operating assets and liabilities:
     Accounts receivable....................................         (615)
     Inventories............................................      (19,659)
     Prepaid expenses and other assets......................         (994)
     Deferred income taxes..................................          (12)
     Accounts payable.......................................        3,748
     Accrued payroll, related expenses, and other...........          156
                                                                 --------
Net cash used in operating activities.......................       (8,339)
INVESTING ACTIVITIES
Acquisitions of property and equipment......................      (17,390)
Proceeds from asset disposals...............................           20
                                                                 --------
Net cash used in investing activities.......................      (17,370)
FINANCING ACTIVITIES
Net increase in due to PACCAR Inc...........................       25,828
Payments of capital lease obligation........................         (399)
Contribution to paid-in capital.............................        3,674
Dividends paid..............................................       (3,365)
                                                                 --------
Net cash provided by financing activities...................       25,738
                                                                 --------
Net increase in cash and cash equivalents...................           29
Cash and cash equivalents, beginning of year................          319
                                                                 --------
Cash and cash equivalents, end of year......................     $    348
                                                                 ========
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid for interest......................................     $    416
Capital lease acquisitions..................................     $  1,000
</TABLE>

                            See accompanying notes.

                                        7
<PAGE>   9

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
                          YEAR ENDED DECEMBER 25, 1998
                            (CURRENCY IN THOUSANDS)

1. ORGANIZATION AND DESCRIPTION OF BUSINESS

     PACCAR Automotive, Inc. (the Company), a wholly owned subsidiary of PACCAR
Inc, is a specialty retailer of automotive aftermarket parts and accessories. At
December 25, 1998, the Company operated 176 stores in 6 western states as a
fully integrated company under two brand names: Al's Auto Supply operating in
Washington, Idaho, and Oregon; and Grand Auto Supply operating in California,
Nevada, Oregon, Idaho, and Alaska.

     PACCAR Automotive Distribution Company (PADC), the Company's wholly owned
subsidiary, provides warehouse and distribution services to the Company.

     Effective October 1, 1999, the Company, exclusive of certain assets and
liabilities included in the balance sheet, was sold by PACCAR Inc to CSK Auto,
Inc. In conjunction with the sale, the Company's name was changed to Al's and
Grand Auto Supply, Inc.

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

PRINCIPLES OF CONSOLIDATION

     The consolidated financial statements include the accounts of the Company
and its wholly owned subsidiary. All significant intercompany accounts and
transactions are eliminated in consolidation.

USE OF ESTIMATES

     The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the reported amounts of assets and liabilities and
disclosure of contingent assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the
reporting period. Actual results could differ from these estimates.

INVENTORIES

     Inventories are stated at the lower of cost or market, cost being
determined by the last-in, first-out method (LIFO).

PROPERTY AND EQUIPMENT

     Property and equipment are recorded at cost. Depreciation and amortization
are computed primarily using the straight-line method over the estimated useful
lives of the related assets, which range from 5 to 42 years as follows:

<TABLE>
<S>                                                       <C>
Machinery and equipment...............................     5-12 years
Buildings.............................................    34-42 years
</TABLE>

     The cost of assets leased under capital lease arrangements is included in
machinery and equipment and buildings according to the nature of the asset.

GOODWILL

     Goodwill is amortized on a straight-line basis over 25 years. At December
25, 1998, goodwill amounted to $11,305, net of accumulated amortization of
$8,299. Amortization of goodwill was $784 in 1998.

                                        8
<PAGE>   10
                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

ENVIRONMENTAL

     Expenditures that relate to current operations are expensed or capitalized
as appropriate. Expenditures that relate to an existing condition caused by past
operations and which do not contribute to current or future revenue generation
are expensed. Liabilities are recorded when it is probable the Company will be
obligated to pay amounts for environmental site evaluation, remediations, or
related costs, and such amounts can be reasonably estimated.

ADVERTISING

     The Company expenses all advertising costs as incurred. Amounts due under
vendor cooperative advertising agreements are recorded as receivables until
their collection. Advertising expense for the year ended December 25, 1998
totaled approximately $8,300. Advertising revenues under cooperative advertising
agreements totaled $10,100.

INCOME TAXES

     The Company files federal and state income tax returns as a member of a
consolidated group. Any refund or liability for federal and state income tax is
reflected through the intercompany account with PACCAR Inc, which files the
consolidated federal and state income tax returns. PACCAR Inc has adopted a
policy of allocating income tax liabilities and assets among individual members
of the group as if each member was a separate taxpayer.

     Deferred income taxes are recognized for the tax consequences in future
years of differences between the tax basis of assets and liabilities (temporary
differences) and the amounts for financial reporting purposes at each year-end
based on enacted tax laws and statutory rates applicable to the period in which
the temporary differences are expected to affect taxable income. Valuation
allowances are established, when necessary, to reduce deferred tax assets to the
amount expected to be realized. Income tax expense is the tax payable for the
period and the change during the period in deferred tax assets and liabilities.

3. INVENTORIES

<TABLE>
<CAPTION>
                                                          DECEMBER 25,
                                                              1998
                                                          ------------
<S>                                                       <C>
Inventories at FIFO (first-in, first-out) cost..........    $81,073
Less excess of FIFO cost over LIFO cost.................     (3,364)
                                                            -------
                                                            $77,709
                                                            =======
</TABLE>

4. PROPERTY AND EQUIPMENT

     Property and equipment is comprised of the following (in thousands):

<TABLE>
<CAPTION>
                                                          DECEMBER 25,
                                                              1998
                                                          ------------
<S>                                                       <C>
Land....................................................    $  1,661
Buildings and improvements..............................      41,068
Machinery and equipment.................................      48,952
                                                            --------
                                                              91,681
Less accumulated depreciation and amortization..........     (45,261)
                                                            --------
Property and equipment, net.............................    $ 46,420
                                                            ========
</TABLE>

                                        9
<PAGE>   11
                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

     Cost and accumulated amortization of property and equipment under capital
leases totaled $7,408 and $3,200, respectively, at December 25, 1998.
Amortization for the period is included within total depreciation and
amortization of $4,901.

5. LEASES

     The Company leases most of its store locations. Leases expire at various
dates through 2013.

     Future minimum lease obligations under noncancelable leases at December 25,
1998 are as follows:

<TABLE>
<CAPTION>
                                                           OPERATING    CAPITAL
                                                            LEASES      LEASES
                                                           ---------    -------
<S>                                                        <C>          <C>
1999.....................................................   $13,111     $  806
2000.....................................................    11,860        774
2001.....................................................    16,688        704
2002.....................................................     9,516        621
2003.....................................................     8,045        621
Thereafter...............................................    24,744      4,473
                                                            -------     ------
                                                            $83,964     $7,999
                                                            =======     ======
</TABLE>

     Minimum payments on operating leases have not been reduced by aggregate
minimum sublease rentals of $8,529 receivable under noncancelable subleases.
Total rental expense under all leases for the year ended December 25, 1998 was
$9,908. Capital lease obligations include interest of $2,994, which relates to
future periods.

     Certain leases are subject to contingent rental provisions based upon gross
sales at the relevant store location.

6. INCOME TAXES

     The provision (benefit) for income taxes is comprised of the following:

<TABLE>
<CAPTION>
                                                           YEAR ENDED
                                                          DECEMBER 25,
                                                              1998
                                                          ------------
<S>                                                       <C>
Current:
Federal...............................................       $2,675
  State...............................................          358
                                                             ------
                                                              3,033
Deferred:
  Federal.............................................          (53)
  State...............................................           (8)
                                                             ------
                                                                (61)
                                                             ------
Total.................................................       $2,972
                                                             ======
</TABLE>

                                       10
<PAGE>   12
                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

     The following table summarizes the differences between the Company's
provision for income taxes and the expected provision:

<TABLE>
<CAPTION>
                                                           YEAR ENDED
                                                          DECEMBER 25,
                                                              1998
                                                          ------------
<S>                                                       <C>
Income before taxes...................................       $6,989
Federal income tax statutory rate.....................           35%
                                                             ------
Expected provision for federal income taxes...........        2,446
State taxes, net of federal benefit...................          229
Goodwill..............................................          274
Other.................................................           23
                                                             ------
Income taxes..........................................       $2,972
                                                             ======
</TABLE>

     The current and noncurrent deferred tax assets and liabilities consist of
the following:

<TABLE>
<CAPTION>
                                                          DECEMBER 25,
                                                              1998
                                                          ------------
<S>                                                       <C>
Gross deferred tax assets:
Accrued vacation and workers' compensation............       $1,891
  Provision for environmental liabilities.............        2,216
  Capital lease expenditures..........................          286
  Product liability...................................          513
  Provision for bad debts.............................          180
  Other...............................................          424
                                                             ------
Total gross deferred tax assets.......................        5,510
Gross deferred tax liabilities:
  Internally developed software.......................         (905)
  Inventory...........................................         (657)
  Depreciation........................................       (1,789)
  Other...............................................         (296)
                                                             ------
Total gross deferred tax liabilities..................       (3,647)
                                                             ------
Net deferred tax assets...............................       $1,863
                                                             ======
</TABLE>

     The Company believes that no valuation allowance is required for deferred
tax assets in excess of deferred tax liabilities. The amount of the deferred tax
asset considered realizable, however, could be reduced in the near term if
estimates of future taxable income are reduced.

     The Company's federal income tax carryforward has been fully utilized by
PACCAR Inc in prior years in its consolidated income tax return.

7. EMPLOYEE BENEFIT PLANS

     The Company provides various health, welfare, and disability benefits to
its full-time employees, which are funded primarily by Company contributions.
The Company provides postemployment or postretirement health care or life
insurance benefits to 12 employees.

     Substantially all union employees are covered by one of the two
multi-employer defined benefit pension plans. During 1998, the Company
recognized expenses of $540 for these plans.

                                       11
<PAGE>   13
                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

     The Company sponsors a defined contribution profit-sharing plan with a
401(k) feature (the Plan) which is available to all employees of the Company
except those covered under a collective bargaining union agreement. Employees
are eligible to participate in the Plan when they have completed one year of
continuous service and have worked 1,000 hours or more in the previous 12
months. The Company's profit-sharing contribution consists of 3% of an
employee's base salary. This contribution vests after five years of service. In
addition, the Company matches 50% of employee 401(k) contributions, up to 4% of
the participant's base salary, which vests at the end of the year. Participant
contributions are subject to certain restrictions as set forth in the Internal
Revenue Code. The Company's 401(k) matching contributions totaled $250 and
profit-sharing contributions totaled $755 for the year ended December 25, 1998.

8. OTHER NONCURRENT LIABILITIES

     Other noncurrent liabilities are comprised of the following:

<TABLE>
<CAPTION>
                                                          DECEMBER 25,
                                                              1998
                                                          ------------
<S>                                                       <C>
Environmental.........................................      $ 5,000
Product liability.....................................        1,176
Workers' compensation.................................        4,297
Health benefits.......................................          406
Other postemployment benefits.........................          111
                                                            -------
                                                            $10,990
                                                            =======
</TABLE>

9. COMMITMENTS AND CONTINGENCIES

     The Company is a party to various claims and lawsuits arising in the normal
course of business that, in the opinion of management, are not, singularly or in
the aggregate, material to the Company's financial position or results of
operations.

     The Company is involved in various stages of investigations and clean-up
actions related to environmental matters. The Company has provided $5,800 for
the estimated undiscounted costs to investigate and complete clean-up actions
where it is probable that the Company will incur such costs in the future.

     While neither the timing nor the amount of the ultimate costs associated
with future environmental cleanup can be determined, management does not expect
that those matters will have a material adverse effect on the Company's
consolidated financial position.

10. FAIR VALUES OF FINANCIAL INSTRUMENTS

     The Company's financial instruments consist of cash, receivables, payables,
and capital lease obligations. The carrying amounts of these financial
instruments approximate fair value.

11. RELATED-PARTY TRANSACTIONS

     PACCAR Inc charges the Company for certain administrative services it
provides and for the cost of certain PACCAR Inc employees who devote their time
to the Company. These costs are charged to the Company based upon the Company's
specific use of the services and PACCAR Inc's cost. Management considers these
charges reasonable and not significantly different from the costs that would be
incurred if the Company were on a stand-alone basis. Fees for such
administrative services of $3,674 were charged to the Company for the year ended
December 25, 1998. In lieu of payment, PACCAR Inc recognizes these
administrative services as an additional investment in the Company. The Company
expenses such charges and

                                       12
<PAGE>   14
                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

records the investment as an increase in equity. The Company pays a dividend to
PACCAR Inc for its capital invested in the prior year. Cash dividends of $3,365
were paid in 1998.

     The Company maintains a home office account with PACCAR Inc which is
represented by the Due to PACCAR Inc account on the balance sheet. This account
is used to receive cash from store sales and to record payroll expenses paid on
behalf of the Company. These transactions represent the largest volume of
transactions processed through this account.

     The Company participates with PACCAR Inc for the self-insurance of its
product liabilities and workers' compensation as well as for health and other
post employment benefits (OPEBs) for its employees. During 1998, the Company
expensed the following amounts which were reflected as increases to the Due to
PACCAR Inc balance:

<TABLE>
<S>                                                           <C>
Current income taxes........................................  $3,033
Workers' compensation.......................................   1,360
Health, welfare, and OPEB benefits..........................   2,335
Corporate MIS...............................................     505
Building rent, corporate payroll, and other.................     385
Liability insurance premiums................................     556
</TABLE>

     These amounts reflect the Company's portion of expenses incurred by PACCAR
Inc on the Company's behalf.

12. YEAR 2000 (UNAUDITED)

     The Company has evaluated its information technology as it relates to Year
2000 compliance. The Company's project management activities include planning,
assessment, testing, remediation, and implementation, and are designed to ensure
that there are no material adverse effects on core business operations and that
transactions with customers, suppliers, and financial institutions are fully
supported. The Company completed these efforts in June 1999. The associated
costs were not material to the Company.

     While the Company believes its planning, monitoring, and testing efforts
are adequate to address its Year 2000 concerns, there can be no guarantee that
the systems of other companies on which the Company's systems and operations
rely will be converted on a timely basis and will not have a material effect on
the Company. The Company has identified its critical vendors and is monitoring
their Year 2000 compliance programs.

     Overall, the Company's Year 2000 compliance program is ongoing and its
ultimate scope, as well as the consideration of contingency plans, will continue
to be evaluated as new information becomes available.

13. SUBSEQUENT EVENT

     Effective October 1, 1999, the Company was sold by PACCAR Inc to CSK Auto,
Inc. Certain assets and liabilities were excluded from the sale based on the
terms of the agreement.

                                       13
<PAGE>   15

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

                      CONDENSED CONSOLIDATED BALANCE SHEET
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                  SEPTEMBER 25,
                                                                       1999
                                                                ------------------
<S>                                                             <C>
ASSETS
Current assets:
Cash........................................................         $    250
Accounts receivable.........................................            4,131
Inventories.................................................           92,263
Prepaid expenses and other current assets...................              925
                                                                     --------
          Total current assets..............................           97,569
Property and equipment, net.................................           37,369
Deferred income taxes.......................................            2,622
Goodwill and other assets...................................           10,955
                                                                     --------
          Total Assets......................................         $148,515
                                                                     ========
LIABILITIES AND STOCKHOLDER'S EQUITY
Current liabilities:
Accounts payable............................................           26,101
Accrued payroll and related expenses........................            3,828
Other.......................................................            1,895
                                                                     --------
          Total current liabilities.........................           31,824
Capital lease obligation....................................            3,544
Due to PACCAR Inc...........................................           75,844
Other noncurrent liabilities................................            9,307
                                                                     --------
          Total noncurrent liabilities......................           88,695
Stockholder's equity........................................           27,996
                                                                     --------
          Total liabilities and stockholder's equity........         $148,515
                                                                     ========
</TABLE>

                            See accompanying notes.

                                       14
<PAGE>   16

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

               CONDENSED CONSOLIDATED STATEMENT OF INCOME (LOSS)
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                    NINE MONTHS ENDED
                                                              ------------------------------
                                                              SEPTEMBER 25,    SEPTEMBER 25,
                                                                  1999             1998
                                                              -------------    -------------
<S>                                                           <C>              <C>
Net sales...................................................    $176,930         $156,075
Cost of sales...............................................     100,654           88,468
                                                                --------         --------
Gross profit................................................      76,276           67,607
Store direct expenses.......................................      55,235           43,383
Warehouse and distribution expenses.........................      10,814            8,126
General and administrative expenses.........................      11,565           10,162
Goodwill amortization.......................................         588              588
Other (income) and expense..................................         (28)           1,187
                                                                --------         --------
Earnings before income tax..................................      (1,898)           4,161
Income tax expense (benefit)................................        (486)           1,840
                                                                --------         --------
Net income (loss)...........................................    $ (1,412)        $  2,321
                                                                ========         ========
</TABLE>

                            See accompanying notes.

                                       15
<PAGE>   17

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

                 CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                                                    NINE MONTHS ENDED
                                                              ------------------------------
                                                              SEPTEMBER 25,    SEPTEMBER 25,
                                                                  1999             1998
                                                              -------------    -------------
<S>                                                           <C>              <C>
OPERATING ACTIVITIES
Net Income (loss)...........................................    $ (1,412)        $  2,321
Items included in net income not affecting cash:
Depreciation and amortization...............................       4,747            3,547
Gain on fixed asset sales...................................        (704)              39
Change in operating assets and liabilities
(Increase) decrease in assets other than cash and
  equivalents:
Receivables.................................................        (525)             248
Inventories.................................................     (14,556)          (9,911)
Other.......................................................      (2,152)           1,315
Increase (decrease) in liabilities:
Accounts payable and accrued expenses.......................      (8,078)          (1,212)
Other.......................................................       2,188             (210)
                                                                --------         --------
Net cash provided (used) from operating activities..........     (20,491)          (3,864)
                                                                --------         --------
INVESTING ACTIVITIES
Acquisition of property, plant and equipment................      (3,937)         (10,066)
Proceeds from asset disposals...............................         119               15
                                                                --------         --------
Net cash used in investing activities.......................      (3,818)         (10,051)
                                                                --------         --------
FINANCING ACTIVITIES
Net increase (decrease) in PACCAR Inc.......................      25,267           13,746
Net increase (decrease) in capital lease obligations........      (1,041)             700
Contributed capital.........................................       3,660            2,809
Dividends paid..............................................      (3,674)          (3,365)
                                                                --------         --------
Net cash provided by financing activities...................      24,211           13,890
                                                                --------         --------
Net increase (decrease) in cash and cash equivalents........         (98)             (25)
Cash and cash equivalents at beginning of year..............         348              319
                                                                --------         --------
Cash and cash equivalents at end of year....................    $    250         $    294
                                                                ========         ========
</TABLE>

                            See accompanying notes.

                                       16
<PAGE>   18

                     PACCAR AUTOMOTIVE, INC. AND SUBSIDIARY

              NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS
                                  (UNAUDITED)
                               SEPTEMBER 25, 1999

1. ORGANIZATION AND DESCRIPTION OF BUSINESS

     PACCAR Automotive, Inc. (the Company), a wholly-owned subsidiary of PACCAR
Inc, is a specialty retailer of automotive aftermarket parts and accessories. At
September 25, 1999, the Company operated 194 stores in 6 western states as a
fully integrated company under two brand names: Al's Auto Supply operating in
Washington, Idaho, and Oregon; and Grand Auto Supply operating in California,
Nevada, Oregon, Idaho, and Alaska.

     PACCAR Automotive Distribution Company (PADC), the Company's wholly owned
subsidiary, provides warehouse and distribution services to the Company.

     Effective October 1, 1999, the Company was sold by PACCAR Inc to CSK Auto,
Inc. In conjunction with the sale, the Company's name was changed to Al's and
Grand Auto Supply, Inc. The exclusion of certain assets and liabilities from the
sale transaction has been reflected in these financial statements.

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

PRINCIPLES OF CONSOLIDATION

     The consolidated financial statements include the accounts of the Company
and its wholly owned subsidiary. All significant intercompany accounts and
transactions are eliminated in consolidation.

USE OF ESTIMATES

     The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the reported amounts of assets and liabilities and
disclosure of contingent assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the
reporting period. Actual results could differ from these estimates.

INVENTORIES

     Inventories are stated at the lower of cost or market, cost being
determined by the last-in, first-out method (LIFO).

3. BASIS OF PRESENTATION

     The unaudited consolidated financial statements included herein were
prepared by the Company pursuant to the rules and regulations of the Securities
and Exchange Commission, but do not include all information and footnotes
required by generally accepted accounting principles. In the opinion of
management, the condensed consolidated financial statements reflect all
adjustments, which are of a normal recurring nature, necessary for a fair
presentation of the Company's financial position and the results of its
operations and cash flows. The accompanying consolidated financial statements
should be read in conjunction with the consolidated financial statements and
related notes thereto for the fiscal year ended December 25, 1998.

                                       17
<PAGE>   19

                      CSK AUTO CORPORATION AND SUBSIDIARY

       PRO FORMA CONDENSED CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)

INTRODUCTION

     Effective October 1, 1999, the Company, through its wholly-owned
subsidiary, CSK Auto, Inc., acquired all of the issued and outstanding shares of
common stock of Al's and Grand Auto Supply, Inc., formerly known as PACCAR
Automotive, Inc. ("PAI") for a cash price of $144.9 million, plus acquisition
costs of approximately $0.2 million. The Company funded the purchase price
principally from borrowing under an amendment and restatement of its senior
credit facility.

     The unaudited pro forma condensed consolidated financial statements are
based on the historical consolidated financial statements of the respective
companies. These unaudited pro forma condensed consolidated financial
statements, including the notes thereto, are qualified in their entirety by
reference to, and should be read in conjunction with, the audited financial
statements, including the notes thereto, of the Company, as included in the
Company's Annual Report on Form 10-K filed on April 28, 1999, and PAI which are
included herein.

     The accompanying pro forma information for the fiscal year ended January
31, 1999 reflects the business combination as if it had occurred on February 2,
1998 (the first day of the Company's 1998 fiscal year). The accompanying pro
forma information for the nine-month period ended October 31, 1999 reflects: (1)
the actual results of the acquired business from October 1, 1999 (the actual
date of the business combination) and (2) the pro forma results of the acquired
business as if the combination had occurred on February 1, 1999 (the first day
of the Company's 1999 fiscal year). In both cases, the fiscal periods presented
are those used by the Company. They have been combined with the closest fiscal
period of the acquired business, which are the year ended December 25, 1998 (in
the case of fiscal 1998), and the eight-months ended September 25, 1999 (in the
case of the Company's nine-months ended October 31, 1999).

     Pro forma balance sheet information has not been presented because the
business combination was completed and has already been reflected in the
unaudited balance sheet of the Company included in its quarterly report on Form
10-Q for the quarter ended October 31, 1999.

     The purchase accounting information included herein is preliminary and has
been made solely for the purposes of developing the unaudited pro forma
condensed consolidated financial information. The pro forma information is
presented for illustrative purposes only and is not necessarily indicative of
the financial position or results of operations which would have been reported
had the acquisition and related borrowings actually occurred as of February 2,
1998, or February 1, 1999, nor is it necessarily indicative of future financial
position or results of operations. Although cost savings and other future
synergy benefits of the combined companies are expected, no such benefits are
reflected in these pro forma condensed financial statements.

                                       18
<PAGE>   20

                      CSK AUTO CORPORATION AND SUBSIDIARY

               PRO FORMA CONDENSED CONSOLIDATED INCOME STATEMENT
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                          CSK AUTO         AL'S AND GRAND
                                         CORPORATION      AUTO SUPPLY, INC.                    CSK AUTO
                                      FISCAL YEAR ENDED   FISCAL YEAR ENDED      PRO FORMA    CORPORATION
                                      JANUARY 31, 1999    DECEMBER 25, 1998     ADJUSTMENTS    PRO FORMA
                                      -----------------   -----------------     -----------   -----------
<S>                                   <C>                 <C>                   <C>           <C>
Net sales...........................     $1,004,385           $212,050                        $1,216,435
Cost of sales.......................        531,073            129,898                           660,971
                                         ----------           --------           --------     ----------
Gross profit........................        473,312             82,152                 --        555,464
Other costs and expenses:
  Operating and administrative......        391,863             74,811           $ (1,807)(a)    464,867
  Transition and integration........          3,075                 --                             3,075
  Write-off of unamortized
     management fee.................          3,643                 --                             3,643
  Goodwill amortization.............             --                784              1,960(b)       2,744
  Secondary stock offering costs....            770                 --                               770
                                         ----------           --------           --------     ----------
Operating profit....................         73,961              6,557               (153)        80,365
Interest expense....................         30,730                 --             13,013(c)      43,743
Other (income)......................             --               (432)                             (432)
                                         ----------           --------           --------     ----------
Income before income taxes and
  extraordinary loss................         43,231              6,989            (13,166)        37,054
Income tax expense..................         15,746              2,972             (5,222)(d)     13,496
                                         ----------           --------           --------     ----------
Income before extraordinary loss....         27,485              4,017             (7,944)        23,558
Extraordinary loss, net of tax......         (6,767)                                              (6,767)
                                         ----------           --------           --------     ----------
Net income..........................     $   20,718           $  4,017           $ (7,944)    $   16,791
                                         ==========           ========           ========     ==========
Basic earnings per share............           0.78                                                 0.63
Weighted average shares.............     26,722,322                                           26,722,322
Diluted earnings per share..........           0.75                                                 0.61
Weighted average shares.............     27,640,099                                           27,640,099
</TABLE>

                            See accompanying notes.
                                       19
<PAGE>   21

                      CSK AUTO CORPORATION AND SUBSIDIARY

               PRO FORMA CONDENSED CONSOLIDATED INCOME STATEMENT
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                   NINE MONTHS ENDED   EIGHT MONTHS ENDED
                                   OCTOBER 31, 1999    SEPTEMBER 25,1999
                                       CSK AUTO          AL'S AND GRAND        PRO FORMA     PRO FORMA
                                      CORPORATION      AUTO SUPPLY, INC.      ADJUSTMENTS    COMBINED
                                   -----------------   ------------------     -----------   -----------
<S>                                <C>                 <C>                    <C>           <C>
Net sales........................     $   903,044           $158,762           $     --     $ 1,061,806
Cost of sales....................         469,790            100,023                 --         569,813
                                      -----------           --------           --------     -----------
Gross profit.....................         433,254             58,739                 --         491,993
Other costs and expenses:
  Operating and administrative...         345,865             59,616             (1,216)(a)     404,265
  Transition and integration.....           4,170                 --                 --           4,170
  Goodwill amortization..........             719                523              1,319(b)        2,561
                                      -----------           --------           --------     -----------
Operating profit.................          82,500             (1,400)              (103)         80,997
Interest expense.................          27,016                 --              8,759(c)       35,775
Other (income)...................              --               (204)                --            (204)
                                      -----------           --------           --------     -----------
Income before income taxes and
  extraordinary loss.............          55,484             (1,196)            (8,862)         45,426
Income tax expense...............          21,261               (246)            (3,608)(d)      17,407
                                      -----------           --------           --------     -----------
Income before extraordinary
  loss...........................          34,223               (950)            (5,254)         28,019
Cumulative effect of change in
  accounting principle, net of
  tax............................            (741)                                                 (741)
                                      -----------           --------           --------     -----------
Net income.......................     $    33,482           $   (950)          $ (5,254)    $    27,278
                                      ===========           ========           ========     ===========
Basic earnings per share.........            1.20                                                  0.98
Weighted average shares..........      27,808,757                                            27,808,757
Diluted earnings per share.......            1.17                                                  0.95
Weighted average shares..........      28,708,125                                            28,708,125
</TABLE>

                            See accompanying notes.
                                       20
<PAGE>   22

                      CSK AUTO CORPORATION AND SUBSIDIARY

         NOTES TO PRO FORMA CONDENSED CONSOLIDATED FINANCIAL STATEMENTS
                                  (UNAUDITED)

GENERAL

     Acquisition cost and the preliminary purchase accounting adjustments are
set forth below (in thousands):

<TABLE>
<S>                                                             <C>
Purchase Price..............................................    $144,880
Transaction costs...........................................         250
                                                                --------
          Total acquisition costs...........................    $145,130
                                                                ========
Book value of net assets acquired...........................    $106,596
  Purchase price adjustments:
     Write down of acquired goodwill to estimated fair
       value................................................     (10,912)
     Write down of property and equipment to estimated fair
       value................................................      (6,525)
     Reserve for store closures.............................      (4,025)
     Reserve for employee severance.........................      (1,566)
     Deferred income taxes..................................       1,261
     Net adjustment to reflect inventories at estimated fair
       market values, less normal gross profit and costs to
       sell.................................................         (79)
     Other, net.............................................         (19)
                                                                --------
Book value of net assets acquired after preliminary
  Purchase accounting adjustments...........................      84,731
Net excess of acquisition cost over net assets acquired.....      60,399
                                                                --------
                                                                $145,130
                                                                ========
</TABLE>

                                       21
<PAGE>   23

                      CSK AUTO CORPORATION AND SUBSIDIARY

   NOTES TO PRO FORMA CONDENSED CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)

PRO FORMA ADJUSTMENTS ARE AS FOLLOWS:

a) Reflects the net adjustment resulting from: (1) the elimination of
   depreciation expense from the historical financial statements of Al's & Grand
   Auto Supply, and (2) the inclusion of adjusted depreciation expense resulting
   from the acquisition. Property and equipment balances reflect an adjustment
   to estimated fair market value upon the date of acquisition. For pro forma
   purposes, depreciation expense has been calculated on a straight-line basis
   over the estimated useful lives of the related assets, which range from 5 to
   25 years, or for leasehold improvements the shorter of the base lease term or
   estimated useful life.

b) Reflects the net adjustment resulting from: (1) the elimination of goodwill
   amortization from the historical financial statements of Al's & Grand Auto
   Supply, and (2) the inclusion of adjusted goodwill amortization resulting
   from the acquisition. Goodwill is approximately $60.4 million and reflects
   the excess of purchase cost of the acquired business over the net assets
   acquired, based on a preliminary purchase price allocation. Goodwill has been
   amortized on a straight-line basis utilizing a life of 30 years.

c) Reflects the sum of: (1) the estimated increase in interest expense resulting
   from borrowings undertaken to complete the acquisition, and (2) the increase
   in amortization of debt offering costs resulting from costs incurred to
   obtain the amendment and restatement of the Company's credit facilities to
   finance the acquisition. Interest has been computed at an assumed rate of
   8.2%, which approximates the Company's effective incremental interest rate
   had the debt been outstanding during the periods indicated. Debt offering
   costs have been amortized on an effective-interest method over the remaining
   life of the associated indebtedness.

d) Reflects the income tax impact of the pro forma adjustments, utilizing an
   effective tax rate of approximately 36.4% for the fiscal year 1998 and 38.3%
   for the nine-month period ended October 31, 1999.

                                       22
<PAGE>   24

                                   SIGNATURES

     Pursuant the to requirements of the Securities Exchange Act of 1934, the
registrant has Caused this report to be signed on its behalf by the undersigned
hereunto duly authorized.

                                          CSK AUTO CORPORATION

                                          By: /s/ DON W. WATSON
                                            ------------------------------------
                                            Don Watson
                                            Chief Financial Officer

Date: December 15, 1999

                                       23
<PAGE>   25

                                 EXHIBIT INDEX

<TABLE>
<C>    <S>
 2.1*  Stock Purchase Agreement between CSK Auto, Inc., an Arizona
       corporation, and PACCAR Inc, a Delaware corporation, dated
       as of August 20, 1999.
 4.1*  Third Amended and Restated Credit Agreement, dated as of
       September 30, 1999, among CSK Auto, Inc., The Chase
       Manhattan Bank, DLJ Capital Funding, Inc., Lehman Commercial
       Paper Inc. and the lenders from time to time parties
       thereto.

 23.1  Consent of Ernst & Young LLP
</TABLE>

---------------
* Previously filed