<PAGE>   1
                                                                  EXHIBIT 10.105


                            AGREEMENT AND AMENDMENT

                           dated as of March 31, 1999

                                     among

                       FINANCIAL SECURITY ASSURANCE INC.,

                     NATIONAL FINANCIAL AUTO FUNDING TRUST,

                         HARRIS TRUST AND SAVINGS BANK,

                                     to the

           FIRST AMENDED AND RESTATED MASTER SPREAD ACCOUNT AGREEMENT


                           dated as of March 31, 1998

                   and to the supplements thereto designated

               SERIES 1996-1 SUPPLEMENT, SERIES 1997-1 SUPPLEMENT

                          AND SERIES 1998-1 SUPPLEMENT

                        each dated as of March 31, 1998


<PAGE>   2

        AGREEMENT AND AMENDMENT TO THE FIRST AMENDED AND RESTATED MASTER
         SPREAD ACCOUNT AGREEMENT AND TO THE SERIES SUPPLEMENTS THERETO

THIS AGREEMENT AND AMENDMENT, dated as of March 31, 1999 (this "Amendment"),
among FINANCIAL SECURITY ASSURANCE INC., a New York stock insurance company
("Financial Security"), NATIONAL FINANCIAL AUTO FUNDING TRUST, a Delaware
business trust (the "Transferor"), and HARRIS TRUST AND SAVINGS BANK, an
Illinois banking corporation ("Harris"), in its capacities as trustee under
each Securitization Agreement and as Collateral Agent, to (i) the FIRST AMENDED
AND RESTATED MASTER SPREAD ACCOUNT AGREEMENT, dated as of March 31, 1998, among
Financial Security, the Transferor and Harris, in its capacities as trustee
under each Securitization Agreement and as Collateral Agent (as amended as of
the date hereof (including by this Amendment) and as the same may be further
amended, amended and restated, supplemented or otherwise modified from time to
time in accordance with the terms thereof, the "Master Spread Account
Agreement") and (ii) to the SERIES 1996-1 SUPPLEMENT, SERIES 1997-1 SUPPLEMENT
AND SERIES 1998-1 SUPPLEMENT, each dated as of March 31, 1998, in each case
among Financial Security, the Transferor and Harris, to the First Amended and
Restated Master Spread Account Agreement (as amended as of the date hereof
(including by this Amendment) and as the same may be further amended, amended
and restated, supplemented or otherwise modified from time to time in
accordance with the terms thereof, the "Series 1996-1 Supplement", "Series
1997-1 Supplement" and "Series 1998-1 Supplement", respectively; the Series
1996-1 Supplement, the Series 1997-1 Supplement and the Series 1998-1
Supplement, each a "Series Supplement" and, collectively, the "Series
Supplements").

                                    RECITALS

         WHEREAS, Financial Security, the Transferor and Harris have each
entered into the Master Spread Account Agreement, the Series 1996-1 Supplement,
the Series 1997-1 Supplement and the Series 1998-1 Supplement (for purposes of
this Amendment, Financial Security, the Transferor and Harris are each a
"Party" and, collectively, the "Parties"), and each of the Parties desire to
hereby amend the Master Spread Account Agreement and each of the Series
Supplements in certain respects as provided below.

         WHEREAS, pursuant to Section 8.03 of the Master Spread Account
Agreement, such Agreement and the Series Supplements may be amended or otherwise
modified from time to time in writing by each of the parties thereto.


                                       1
<PAGE>   3

                                   AGREEMENTS

         In consideration of the premises set forth above, and for other good
and valuable consideration, the adequacy, receipt and sufficiency of which each
of the Parties hereto hereby acknowledges, the Parties hereto hereby agree as
follows:

                                   ARTICLE I

                                  DEFINITIONS

         SECTION 1.1 Defined Terms. Unless defined in this Amendment,
capitalized terms used in this Amendment (including in the preamble and the
recitals hereto) shall have the meaning assigned to such terms in the Master
Spread Account Agreement.

                                   ARTICLE II

                                   AMENDMENTS

         SECTION 2.1. Amendment to Section 1.01 to the Master Spread Account
Agreement and Section 1.1 of the Series Supplements.

         (a) The following definition set forth in Section 1.01 of the Master
Spread Account Agreement is hereby amended by deleting the definition set forth
therein in its entirety and substituting therefor the following:

                  "Requisite Amount" means, with respect to the Series 1995-1
         Certificates, as of any Reporting Date after giving effect to any
         distributions of the Certificate Distributable Amount to be made on
         the related Distribution Date, (i) if no Insurance Agreement Event of
         Default shall have occurred as of such Reporting Date, the lesser of
         (A) the greater of (1) 11.0% of the Series 1995-1 Balance and (2)
         $840,000, and (B) the greater of (1) the Certificate Balance as of
         such Reporting Date, and (2) $100,000; provided, if (x) the Chase
         Manhattan Bank Delaware, not in its individual capacity but as Trustee
         of the Transferor, has transferred an amount equal to the total
         Retransfer Amount (as defined in Section 9.01 of the Series 1995-1
         Securitization Agreement) to the Trustee on or prior to such Reporting
         Date and such amount together with any other amounts made available by
         the Transferor to the Trustee for such purpose have been used to fully
         pay the Certificate Balance and any amounts due and payable with
         respect to the Certificates as of such Reporting Date, in each case
         pursuant to Section 9.01 of the Series 1995-1 Securitization
         Agreement, and (y) all Secured Obligations due and payable to
         Financial Security and Trustee as of such Reporting Date have been
         fully paid, then for purposes of this clause (i) the Requisite Amount
         shall be an amount equal to $100,000 as of such Reporting Date, and
         (ii) if an Insurance Agreement Event of Default shall have occurred as
         of such Reporting Date, an unlimited amount."


                                       2
<PAGE>   4

         (b) The following definition set forth in Section 1.1 of the Series
1996-1 Supplement is hereby amended by deleting the definition set forth
therein in its entirety and substituting therefor the following:

                  "Requisite Amount" means, with respect to the Series 1996-1
         Certificates, as of any Reporting Date after giving effect to any
         distributions of the Certificate Distributable Amount to be made on
         the related Distribution Date, (i) if no Insurance Agreement Event of
         Default shall have occurred as of such Reporting Date, the lesser of
         (A) the greater of (1) 11.0% of the Series 1996-1 Balance, and (2)
         $1,364,791.20, and (B) the greater of (1) the Certificate Balance as
         of such Reporting Date and (2) $100,000; provided, if (x) the
         Transferor has transferred an amount equal to the total Retransfer
         Amount (as defined in Section 9.01 of the Series 1996-1 Securitization
         Agreement) to the Trustee on or prior to such Reporting Date and such
         amount together with any other amounts made available by the
         Transferor to the Trustee for such purpose have been used to fully pay
         the Certificate Balance and any amounts due and payable with respect
         to the Certificates as of such Reporting Date, in each case pursuant
         to Section 9.01 of the Series 1996-1 Securitization Agreement, and (y)
         all Secured Obligations due and payable to Financial Security and
         Trustee as of such Reporting Date have been fully paid, then for
         purposes of this clause (i) the Requisite Amount shall be an amount
         equal to $100,000 as of such Reporting Date, and (ii) if an Insurance
         Agreement Event of Default shall have occurred as of such Reporting
         Date, an unlimited amount."

         (c) The following definition set forth in Section 1.1 of the Series
1997-1 Supplement is hereby amended by deleting the definition set forth
therein in its entirety and substituting therefor the following:

                  "Requisite Amount" means, with respect to the Series 1997-1
         Notes, as of any Reporting Date after giving effect to any
         distributions of principal on the Series 1997-1 Notes to be made on
         the related Distribution Date, (i) if no Insurance Agreement Event of
         Default shall have occurred as of such Reporting Date, the lesser of
         (A) the greater of (1) 11% of the Series 1997-1 Balance and (2)
         $2,205,204.40, and (B) the greater of (1) the outstanding principal
         amount of the Series 1997-1 Notes as of such Reporting Date after
         giving effect to any distributions of principal to be made thereon on
         the related Distribution Date and (2) $100,000; provided, if (x) the
         Transferor has deposited to the Collection Account an amount equal to
         the aggregate Purchase Amount (as determined by the appraiser referred
         to in Section 11.1 of the Series 1997-1 Sale and Servicing Agreement)
         for the Receivables pursuant to Section 11.1 of the Series 1997-1
         Sale and Servicing Agreement on or prior to such Reporting Date, (y)
         the Notes have been redeemed for an amount equal to the Redemption
         Price pursuant to Section 10.01 of the Series 1997-1 Indenture on or
         prior to such Reporting Date and all amounts due and payable on the
         Notes as of such Reporting Date have been fully paid and (z) all
         Secured Obligations due and payable to Financial Security and the
         Trustee as of such Reporting Date have been fully paid, then for
         purposes of this clause (i) the Requisite Amount shall be an amount
         equal to $100,000 as of such Reporting Date, and (ii) if an Insurance
         Agreement Event of Default shall have occurred as of such Reporting
         Date, an unlimited amount."


                                       3
<PAGE>   5

         (d) The following definition set forth in Section 1.1 of the Series
1998-1 Supplement is hereby amended by deleting the definition set forth
therein in its entirety and substituting therefor the following:

                  "Requisite Amount" means, with respect to the Series 1998-1
         Notes, as of any Reporting Date after giving effect to any
         distributions of principal on the Series 1998-1 Notes to be made on
         the related Distribution Date, (i) if no Insurance Agreement Event of
         Default shall have occurred as of such Reporting Date, the lesser of
         (A) the greater of (1) 11.0% of the Series 1998-1 Balance and (2)
         $2,340,659.34, and (B) the greater of (1) the outstanding principal
         amount of the Series 1998-1 Notes as of such Reporting Date after
         giving effect to any distributions of principal to be made thereon on
         the related Distribution Date and (2) $100,000; provided, if (x) the
         Transferor has deposited to the Collection Account an amount equal to
         the aggregate Purchase Amount (as determined by the appraiser referred
         to in Section 11.1 of the Series 1998-1 Sale and Servicing Agreement)
         for the Receivables pursuant to Section 11.1 of the Series 1998-1
         Sale and Servicing Agreement on or prior to such Reporting Date, (y)
         the Notes have been redeemed for an amount equal to the Redemption
         Price pursuant to Section 10.01 of the Series 1998-1 Indenture on or
         prior to such Reporting Date and all amounts due and payable on the
         Notes as of such Reporting Date have been fully paid and (z) all
         Secured Obligations due and payable to Financial Security and the
         Trustee as of such Reporting Date have been fully paid, then for
         purposes of this clause (i) the Requisite Amount shall be an amount
         equal to $100,000 as of such Reporting Date, and (ii) if an Insurance
         Agreement Event of Default shall have occurred as of such Reporting
         Date, an unlimited amount."

         (e) For the March 1999 and April 1999 Due Periods, the Requisite Amount
with respect to the Series 1995-1 Certificates, Series 1996-1 Certificates,
Series 1997-1 Notes and the 1998-1 Notes shall equal the sum of (i) the
"Requisite Amount" as defined without reference to this Section 2.1(e) and (ii)
$500,000.

         SECTION 2.2. Release of Funds from Spread Accounts. Notwithstanding any
provision to the contrary contained herein or in the First Amended and Restated
Master Spread Agreement or the Series Supplements, all amounts otherwise
distributable from the Spread Accounts pursuant to the First Amended and
Restated Master Spread Account Agreement or this Agreement will be retained in
such Spread Accounts until such time as the Chase Manhattan Bank Delaware, not
in its individual capacity but as Trustee of the Transferor has delivered (or
caused to be delivered) to Financial Security a report regarding certain
proposed adjustments to the Series 1995-1 Balance, the Series 1996-1 Balance,
the Series 1997-1 Balance and the Series 1998-1 Balance and Financial Security
has consented to such proposed adjustments (such adjustments, as consented to by
Financial Security, the "Reconciliation"), which consent shall not be
unreasonably withheld; provided, however, that all amounts deposited to the
Spread Accounts on or after the April 1999 Distribution Date and prior to the
Release Date (as defined below) shall be promptly remitted to the Reversionary
Holder unless there shall have occurred and be continuing an Insurance Agreement
Event of Default. On the first Distribution Date following the first full Due
Period after the Due Period in which Financial Security gives its


                                       4
<PAGE>   6
consent to such proposed adjustments (such first Distribution Date, the "Release
Date"), funds on deposit in the Spread Account (including amounts retained in
the Spread Accounts pursuant to the preceding sentence) shall be released to the
Reversionary Holder or such party as shall have been designated by the
Reversionary Holder to the extent and only to the extent the Reversionary Holder
is entitled to a Distribution under Section 3.03 of the First Amended and
Restated Master Spread Agreement and the Series Supplements. The parties hereto
further agree that funds on deposit in the Collection Accounts for the
transactions to which the Series Supplements relate shall, to the extent such
funds would have been released on a prior Distribution Date but for the
discrepancies in principal balances of the receivables that were the subject of
the Reconciliation (such funds, the "Prior Period Funds"), be applied on the
Release Date pursuant to the distribution provisions of the Pooling and
Servicing Agreements relating to the Series 1995-1 and Series 1996-1
transactions and the Sale and Servicing Agreements relating the Series 1997-1
transaction and the Series 1998-1 transaction and, to the extent such funds as
deposited to the Spread Accounts, shall be released from the Spread Accounts if
and to the extent provided in the preceding sentence.

                                  ARTICLE III

                           CONDITION TO EFFECTIVENESS

         SECTION 3.1. Execution and Delivery. This Amendment shall become
effective upon receipt by Financial Security of counterparts hereof executed and
delivered on behalf of each of the Parties hereto.

                                   ARTICLE IV

                                 MISCELLANEOUS

         SECTION 4.1. Ratification. Except as expressly set forth herein, this
Amendment shall not by implication or otherwise limit, impair, constitute a
waiver of, or otherwise affect the rights and remedies of any of the Parties
hereto under the Master Spread Account Agreement or the Series Supplements, nor
alter, modify, amend or in any way affect any of the terms, conditions,
obligations, covenants or agreements contained in the Master Spread Account
Agreement or the Series Supplements, all of which are hereby ratified and
affirmed in all respects by each of the Parties hereto and shall continue in
full force and effect. This Amendment shall apply and be effective only with
respect to the provisions of the Master Spread Account Agreement and each
Series Supplement specifically referred to herein and any references in the
Master Spread Account Agreement or any Series Supplement or to the provisions
of such Master Spread Account Agreement or Series Supplement specifically
referred to herein shall be to such provisions as amended by this Amendment.

         SECTION 4.2. Counterparts. This Amendment may be executed in any
number of counterparts, each of which so executed shall be deemed to be an
original, but all of such counterparts shall together constitute but one and the
same instrument.


                                       5
<PAGE>   7

         SECTION 4.3. GOVERNING LAW. THIS AMENDMENT SHALL BE CONSTRUED IN
ACCORDANCE WITH THE LAW OF THE STATE OF NEW YORK (WITHOUT GIVING EFFECT TO THE
PROVISIONS THEREOF REGARDING CONFLICTS OF LAWS), AND THE OBLIGATIONS, RIGHTS
AND REMEDIES OF THE PARTIES HERETO SHALL BE DETERMINED IN ACCORDANCE WITH SUCH
LAW.

         SECTION 4.4. Waiver of Notice. Each of the Parties hereto waives any
prior notice and any notice period that may be required by any other agreement
or document in connection with the execution of this Amendment.

         SECTION 4.5. Headings. The headings of Sections contained in this
Amendment are provided for convenience only. They form no part of this
Amendment, the Master Spread Account Agreement or Series Supplements and shall
not affect the construction or interpretation of this Amendment, the Master
Spread Account Agreement or the Series Supplements or any provisions hereof or
thereof.

         SECTION 4.6. Directions by Instructing Party.

                  (a) NAFI, by its execution of this Amendment, hereby directs
Chase Manhattan Bank Delaware, as owner trustee of National Financial Auto
Funding Trust, to consent to this Amendment and to execute and deliver this
Amendment.

                  (b) Financial Security, by its execution and delivery of this
letter, hereby consents to this Amendment and hereby directs Harris as trustee
to the Master Spread Account Agreement and Series Supplement, to consent to this
Amendment and to execute and deliver this Amendment.


                                       6
<PAGE>   8

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed by their respective duly authorized officers as of the day and
year first above written.

                                   FINANCIAL SECURITY ASSURANCE INC.


                                   By: /s/ ERROL UHR
                                       -----------------------------------
                                       Name:  Errol Uhr
                                       Title: Managing Director

                                   NATIONAL FINANCIAL AUTO FUNDING TRUST


                                     By: CHASE MANHATTAN BANK/DELAWARE,
                                         not in its individual capacity,
                                         but solely as owner trustee of the
                                         National Financial Auto Funding Trust


                                       By: /s/ DENIS KELLY
                                           -------------------------------
                                           Name:  Denis Kelly
                                           Title: Trust Officer

                                   HARRIS TRUST AND SAVINGS BANK,
                                      as Trustee


                                   By: /s/ ROBERT D. FOLTZ
                                       -----------------------------------
                                       Name:  Robert D. Foltz
                                       Title: Vice President

                                   HARRIS TRUST AND SAVINGS BANK,
                                      as Collateral Agent

                                   By: /s/ ROBERT D. FOLTZ
                                       -----------------------------------
                                       Name:  Robert D. Foltz
                                       Title: Vice President

ACCEPTED AND ACKNOWLEDGED

NATIONAL AUTO FINANCE COMPANY, INC.

By: /s/ KEITH B. STEIN
    --------------------------------
    Name:  Keith B. Stein
    Title: Vice Chairman and Chief
            Executive Officer


                                       7