Document:

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                                                                Exhibit 10(a)(5)

                    International Truck & Engine Corporation
                               4201 Winfield Road
                              Warrenville, IL 60555
                                 (630) 753-5000

                                December 29, 2003

Core Molding Technologies, Inc.
800 Manor Park Drive
Columbus, Ohio 43228
Attention:  Herman F. Dick, Jr.

     RE:  PAYOFF OF THAT CERTAIN SECURED PROMISSORY NOTE DATED AS OF DECEMBER
          31, 1996, AS THEREBY AMENDED FROM TIME TO TIME (COLLECTIVELY REFERRED
          TO AS THE "SECURED NOTE"), IN THE ORIGINAL PRINCIPAL AMOUNT OF
          $25,504,000, ISSUED BY CORE MOLDING TECHNOLOGIES, INC. (F/K/A CORE
          MATERIALS CORPORATION), A DELAWARE CORPORATION ("CORE") TO
          INTERNATIONAL TRUCK & ENGINE CORPORATION (F/K/A NAVISTAR INTERNATIONAL
          TRANSPORTATION CORP.), A DELAWARE CORPORATION ("INTERNATIONAL")

Ladies and Gentlemen:

         This Letter Agreement acknowledges your request for a payoff amount for
all of Core's obligations to International as of December 29, 2003 (the "Payoff
Date"), pursuant to the Secured Note and all other related documents executed in
connection therewith and, in each case, as amended from time to time, for the
purpose of repaying in full all of the obligations and liabilities of Core to
International pursuant to the Secured Note. Capitalized terms used but not
otherwise defined herein shall have the corresponding meanings set forth in the
Secured Note.

         As of the Payoff Date, the amount of Core's outstanding obligations
(including, without limitation, all accrued and unpaid principal and interest)
under the Secured Note is $18,789,685.87 (the "Payoff Amount").

         The Payoff amount will be comprised of $18,589,685.87 in cash and a
$200,000 unsecurred note executed and delivered on December 29, 2003.

         The cash Payoff Amount should be sent by wire transfer to International
pursuant to the instructions set forth below by 3:00 p.m. EST on the Payoff
Date:

                           ABA No.:          0710-0003-9
                           Account No.:      8188002125
                           Account Name:     International Truck & Engine Corp.
                           Bank:             Bank of America, Illinois

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         If the Payoff Amount is not received in immediately available funds by
3:00 p.m. EST on the Payoff Date, the amounts necessary to repay all of such
indebtedness and other obligations shall be increased by $4,013.18 per day.

         Upon receipt by International of the Payoff Amount, International
hereby acknowledges and agrees that:

         (a)      All Indebtedness or other obligations of Core to International
                  pursuant to the Secured Note will be satisfied and paid in
                  full;

         (b)      International will immediately release all Liens relating to
                  all real or personal property of Core;

         (c)      International will promptly prepare, execute and deliver to
                  Core releases, satisfaction of mortgages and UCC-3 termination
                  statements terminating all Liens against Core's property held
                  by International;

         (d)      International will promptly deliver to Core the original
                  Secured Note marked "paid in full" or "cancelled;" and

         (e)      International will promptly execute and deliver such other
                  documents or instruments, in form and substance reasonably
                  satisfactory to Core, and to take any other actions reasonably
                  requested by Core for the purpose of effectuating the intent
                  of this Payoff Letter.

         This Letter Agreement shall be deemed to be a contract made under and
for all purposes shall be governed by and construed in accordance with the laws
of the State of Ohio, without regard to the principles of conflicts of law.

         This Letter Agreement may be executed by the parties hereto
individually or in any combination, in one or more counterparts, each of which
shall be deemed to be one and the same agreement.

                            [Signature page follows]

                                       2
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         IN WITNESS WHEREOF, the undersigned has executed this Letter Agreement
as of the date first set forth above.

                                            INTERNATIONAL TRUCK &
                                            ENGINE CORPORATION, a Delaware
                                            corporation (f/k/a Navistar
                                            International Transportation Corp.)

                                            By:  /s/ T. M. Endsley
                                                 ---------------------------
                                            Name:  Terry M. Endsley
                                            Title:  Vice President & Treasurer

ACCEPTED AND AGREED TO THIS 29TH DAY
OF DECEMBER, 2003

CORE MOLDING TECHNOLOGIES, INC.,
a Delaware corporation (f/k/a Core Materials
Corporation)

By:  /s/ Herman F. Dick Jr.
     ----------------------
      Herman F. Dick, Jr.
      Chief Financial Officer

                                       3<PAGE>
                                                                EXHIBIT 10(a)(6)

                         CORE MOLDING TECHNOLOGIES, INC

                            UNSECURED PROMISSORY NOTE
                                 ---------------

$200,000.00                                                   December 29, 2003

       FOR VALUE RECEIVED, Core Molding Technologies, Inc. (f/n/a Core Materials
Corporation), a Delaware corporation (hereinafter referred to as the "Company"),
hereby promises to pay to the order of International Truck & Engine Corporation
(f/n/a Navistar International Transportation Corporation), a Delaware
corporation (hereinafter referred to "International," which term shall include
any subsequent holder hereof), the principal amount of Two Hundred Thousand and
00/100 Dollars ($200,000.00), together with interest thereon calculated from the
date hereof in accordance with the provisions of this Unsecured Promissory Note
(this "Note").

       This Note is being issued in connection with the payoff of that certain
secured promissory note executed by the Company and delivered to International
on December 31, 1996, as thereby amended from time to time.

1. PAYMENTS OF PRINCIPAL AND INTEREST.

   (A) PRINCIPAL PAYMENT. The Company shall pay the entire principal balance of
this Note on December 31, 2004.

   (B) INTEREST. Except as otherwise expressly provided herein, interest shall
accrue at the rate of eight percent (8.0%) per annum, (computed on the basis of
a 360-day year and the actual number of days elapsed in any year) on the unpaid
principal amount of this Note outstanding from time to time from and including
the date hereof until the date paid, or (if less) at the highest rate then
permitted under applicable law. The Company shall pay to International all
accrued interest on this Note on December 31, 2004.

2. PREPAYMENTS.

   The Company may, without premium or penalty, at any time and from time to
time, prepay all or any portion of the outstanding principal amount of this
Note, provided that the Company has first paid all accrued interest on this
Note.

3.  MISCELLANEOUS

   Payments of any amount required hereunder shall be made in lawful money of
the United States or, as Noteholder, in his sole and absolute discretion, may
accept. All payments of any amount required hereunder shall be credited first
against collection of costs, if any, thereafter against accrued but unpaid late
charges, if any, thereafter against accrued but unpaid interest, if any, and
thereafter against the unpaid balance of the principal amount.

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   The Company agrees to pay Noteholder all costs and expenses, including
reasonable attorneys' fees, paid or incurred by Noteholder in connection with
the collection or enforcement of this Note.
   This Note shall be governed by, interpreted under and construed and enforced
in accordance with the laws of the State of Illinois. Any action to enforce
payment of this note shall be filed and heard solely in Dupage County, Illinois.

   IN WITNESS WHEREOF, this instrument is executed as of the day and year first
above written.

                           CORE MOLDING TECHNOLOGIES, INC

                           By: /s/Herman F. Dick, Jr.
                               ----------------------
                               Herman F. Dick, Jr.
                               Treasurer and Chief Financial Officer

Accepted and agreed to
this 29th day of December, 2003

INTERNATIONAL TRUCK & ENGINE CORPORATION

By: /s/ T. M. Endsley
    -----------------
     Name:  Terry M. Endsley
            ----------------
     Title:  Vice President & Treasurer
             --------------------------

                                      -2-<PAGE>

                                                                EXHIBIT 10(a)(7)

                               AMENDMENT NO. 1 TO

                            UNSECURED PROMISSORY NOTE

         THIS AMENDMENT NO. 1 TO UNSECURED PROMISSORY NOTE (this "Amendment")
entered into as of this 30th day of January 2004, by and between International
Truck & Engine Corporation, a Delaware corporation ("International"), and Core
Molding Technologies, Inc., a Delaware corporation (the "Company").

                                   WITNESSETH:

         WHEREAS, the Company previously executed and delivered to International
that certain Unsecured Promissory Note dated as of December 29, 2003, in the
original principal amount of Two Hundred Thousand and 00/100 Dollars
($200,000.00) (the "Note");

         NOW, THEREFORE, for good and valuable consideration, the receipt of
which is hereby acknowledged, International and the Company desire to amend the
Note and hereby agree as follows:

         1.       Each reference to "Noteholder" in Section 3. MISCELLANEOUS of
the Note shall be stricken and replaced with "International" and any reference
to "his" in such Section 3 shall be stricken and replaced with "it. "

         2.       A new Section 4. PERFORMANCE OF OBLIGATIONS shall be added to
the Note and shall read as follows:

         4.       PERFORMANCE OF OBLIGATIONS.

                  The outstanding principal and interest of this Note will be
         forgiven by International, provided the Company achieves earnings
         before interest and taxes of $3,981,000.00 for the period January 1,
         2004 to December 31, 2004.

         3.       The Company hereby ratifies and confirms the Note, as amended
hereby, in all respects, and, as amended hereby, the terms thereof shall remain
in full force and effect. This Amendment may be attached to and shall form a
part of the Note for all purposes. This Amendment may be executed in two or more
counterparts, each of which shall be deemed to be an original, but all of which
together shall constitute one and the same instrument

         IN WITNESS WHEREOF, this instrument is executed as of the day and year
first above written.

                                        Core Molding Technologies, Inc.

                                        By: /s/ Herman F. Dick Jr.
                                            ----------------------
                                            Herman F. Dick, Jr.
                                            Treasurer and CFO

                                        International Truck & Engine Corp.

                                        By: /s/ T.M. Endsley
                                            -----------------------
                                            Terry Endsley
                                            Vice President and Treasurer

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