<PAGE>

                                                                   Exhibit 10.71

                                                                  EXECUTION COPY

                                 AMENDMENT NO. 5
                                       TO
                             NOTE PURCHASE AGREEMENT

            This AMENDMENT NO. 5 (the "Amendment") dated as of January 31, 2005,
to the Note Purchase Agreement dated as of August 8, 2003 (as amended,
supplemented or otherwise modified hereby and from time to time hereafter, the
"Note Purchase Agreement") by and among Option One Owner Trust 2003-4 (the
"Issuer"), Option One Mortgage Corporation (the "Servicer"), Option One Loan
Warehouse Corporation (the "Depositor"), Falcon Asset Securitization Corporation
("Falcon"), Jupiter Securitization Corporation ("Jupiter"), Preferred
Receivables Funding Corporation ("Prefco" and, together with Falcon and Jupiter,
the "Conduit Purchasers"), the financial institutions party thereto (the
"Committed Purchasers") and JPMorgan Chase Bank, N.A. (successor by merger to
Bank One, NA (Main Office Chicago)) (the "Note Agent"). Capitalized terms used
herein but not specifically defined herein shall have the meanings given to such
terms in the Note Purchase Agreement.

            PRELIMINARY STATEMENTS:

            (1) The Issuer, the Servicer, the Depositor, the Conduit Purchasers,
the Committed Purchasers and the Note Agent are parties to the Note Purchase
Agreement.

            (2) The Issuer has requested that the Purchasers agree to increase
the Maximum Note Principal Balance.

            (3) In consideration of the mutual agreements contained herein, and
for other valuable consideration, receipt of which is hereby acknowledged, the
parties hereto have agreed to amend the Note Purchase Agreement as set forth
herein.

            NOW, THEREFORE, the parties hereto agree as follows:

      SECTION 1. Amendment. Effective as of the date hereof and subject to the
satisfaction of the conditions precedent set forth in Section 2 hereof, the Note
Purchase Agreement is hereby amended as follows:

            (a) The definition of "Maximum Note Principal Balance" set forth in
Section 1.01 of the Note Purchase Agreement is hereby restated in its entirety
as follows:

            "Maximum Note Principal Balance" means (i) from January 31, 2005
            through April 30, 2005, $1,500,000,000 and (ii) thereafter,
            $1,000,000,000, in each case, as such amount may be increased or
            decreased in accordance with the terms of this Agreement.

<PAGE>

            (b) Schedule I to the Note Purchase Agreement is hereby replaced
with Schedule I attached hereto.

      SECTION 2. Conditions of Effectiveness. This Amendment shall become
effective as of the date hereof when, and only when, the Note Agent shall have
received the following:

            (a) an executed counterpart of this Amendment from each of the
parties hereto.

      SECTION 3. Representations and Warranties. Each of the parties hereto
represents and warrants that this Amendment and the Note Purchase Agreement, as
amended by this Amendment, constitute legal, valid and binding obligations of
such Person enforceable against such Person in accordance with their terms,
except as enforceability may be limited by bankruptcy, insolvency or similar
laws affecting the enforcement of creditors' rights generally and general
equitable principles.

      SECTION 4. Reference to and the Effect on the Note Purchase Agreement.

            (a) On and after the effective date of this Amendment, each
reference in the Note Purchase Agreement to "this Agreement", "hereunder",
"hereof", "herein" or words of like import referring to the Note Purchase
Agreement and each reference to the Note Purchase Agreement in any certificate
delivered in connection therewith, shall mean and be a reference to the Note
Purchase Agreement as amended hereby.

            (b) Each of the parties hereto hereby agrees that, except as
specifically amended above, the Note Purchase Agreement is hereby ratified and
confirmed and shall continue to be in full force and effect and enforceable,
except as such enforcement may be limited by applicable bankruptcy, insolvency,
reorganization or other similar laws relating to or limiting creditors' rights
generally and general equitable principles.

      SECTION 5. Costs and Expenses. The Issuer agrees to pay on demand all
reasonable costs and expenses of the Note Agent in connection with the
preparation, execution and delivery of this Amendment and the other instruments
and documents to be delivered in connection herewith, including, without
limitation, the reasonable fees and out-of-pocket expenses of counsel for the
Note Agent with respect thereto and with respect to advising the Note Agent as
to its respective rights and responsibilities hereunder and thereunder.

      SECTION 6. Execution in Counterparts. This Amendment may be executed in
any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed and delivered shall be deemed to be
an original and all of which taken together shall constitute but one and the
same agreement.

      SECTION 7. Governing Law. This Amendment shall be construed in accordance
with, and governed by the laws of the State of New York, without giving effect
to its conflicts of law provisions.

                                      -2-
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            IN WITNESS WHEREOF, the parties have executed this Amendment as of
the day and year first above written.

                                    OPTION ONE OWNER TRUST 2003-4,
                                    as Issuer

                                    By: Wilmington Trust Company, not in its
                                        individual capacity, but solely as
                                        Owner Trustee

                                    By: /s/ Mary Kay Pupillo
                                        -------------------------------
                                            Name:
                                            Title:

                                    OPTION ONE LOAN WAREHOUSE
                                    CORPORATION, as Depositor

                                    By: /s/ C.R. Fulton
                                        -------------------------------
                                        Name:
                                        Title:

                                    OPTION ONE MORTGAGE CORPORATION, as
                                    Servicer

                                    By: /s/ C.R. Fulton
                                        ------------------------------
                                        Name:
                                        Title:

                                 Signature Page
                                       to
                   Amendment No. 4 to Note Purchase Agreement

<PAGE>

                                 FALCON ASSET SECURITIZATION
                                 CORPORATION, as a Conduit Purchaser

                                 By: /s/ Daniel J. Clarke, Jr.
                                     -----------------------------------
                                     Name: Daniel J. Clarke, Jr.
                                     Title: Authorized Signer

                                 JUPITER SECURITIZATION CORPORATION,
                                 as a Conduit Purchaser

                                 By: /s/ Daniel J. Clarke, Jr.
                                     -------------------------------
                                     Name: Daniel J. Clarke, Jr.
                                     Title: Authorized Signer

                                 PREFERRED RECEIVABLES FUNDING
                                 CORPORATION, as a Conduit Purchaser

                                 By: /s/ Daniel J. Clarke, Jr.
                                     ---------------------------------
                                     Name: Daniel J. Clarke, Jr.
                                     Title: Authorized Signer

                                 JPMORGAN CHASE BANK, N.A., successor by merger
                                 to BANK ONE, NA (Main Office Chicago), as a
                                 Committed Purchaser and as Note Agent

                                 By: /s/ Daniel J. Clarke, Jr.
                                     ------------------------------
                                     Name: Daniel J. Clarke, Jr.
                                     Title: Managing Director

                                Signature Page
                                       to
                   Amendment No. 4 to Note Purchase Agreement

<PAGE>

                                                                      SCHEDULE I

                                  COMMITMENTS

<TABLE>
<CAPTION>
          COMMITTED PURCHASER                              COMMITMENT
          -------------------              ---------------------------------------
<S>                                        <C>
JPMorgan Chase Bank, N.A., successor by    (i) from January 31, 2005 through April
merger to Bank One, NA (Main Office        30, 2005, $1,500,000,000 and (ii)
Chicago)                                   thereafter, $1,000,000,000
</TABLE>