Document:

<PAGE>   1
                                                                     EXHIBIT 4.1

                             SUPPLEMENTAL INDENTURE

         SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of
August 29, 2000, among Oxford Automotive, Inc., a Michigan corporation (the
"Company"), the Subsidiary Guarantors (the "Subsidiary Guarantors") under the
Indenture referred to below, and U.S. Bank Trust National Association (formerly
known as First Trust National Association), a national banking corporation, as
trustee under the Indenture referred to below (the "Trustee").

                  WHEREAS the Company has heretofore executed and delivered to
the Trustee an Indenture (as such may be amended from time to time, the
"Indenture"), dated as of June 15, 1997, providing for the issuance of an
aggregate principal amount of $160,000,000 of 10 1/8% Senior Subordinated Notes
Due 2007 (the "Securities");

         WHEREAS pursuant to Section 9.2 of the Indenture, the Trustee, the
Company and the Subsidiary Guarantors may, with the consent of the Holders (as
defined in the Indenture) of at least a majority in principal amount of the
Securities outstanding, execute and deliver this Supplemental Indenture for the
purpose of amending, modifying or changing certain provisions of the Indenture;

         WHEREAS the Company and the Subsidiary Guarantors desire to amend or
eliminate certain provisions of the Indenture as hereinafter set forth; and

         WHEREAS all acts and things necessary to amend the Indenture as
described above and to make this Supplemental Indenture a valid agreement of the
Company and the Subsidiary Guarantors, in accordance with its terms, have been
completed.

         NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Company, the Subsidiary Guarantors and the Trustee mutually covenant and agree
for the equal and ratable benefit of the Holders of the Securities as follows:

         1.       Definitions.

                  (a) Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

                  (b) For all purposes of this Supplemental Indenture, except as
otherwise herein expressly provided or unless the context otherwise requires:
(i) the terms and expressions used herein shall have the same meanings as
corresponding terms and expressions used in the Indenture; and (ii) the words
"herein," "hereof" and "hereby" and other words of similar import used in this
Supplemental Indenture refer to this Supplemental Indenture as a whole and not
to any particular section hereof.

<PAGE>   2

         2.       Amendment to Indenture.  The following sections of the
Indenture are modified as follows:

                  (a)      The following definition is hereby added to Section
                  1.1 of the Indenture:

                  "Domestic Subsidiary" means any Restricted Subsidiary of the
                  Company organized under the laws of any state of the United
                  States of America or the District of Columbia.

                  (b)      Section 4.14 of the Indenture is amended and restated
                  to read as follows:

                  SECTION 4.14. Future Guarantors. The Company shall cause (a)
                  each Domestic Subsidiary that at any time becomes an obligor
                  or guarantor with respect to any Obligations under one or more
                  Bank Credit Agreements and (b) each other Restricted
                  Subsidiary that guarantees the Obligations of the Company or
                  any Domestic Subsidiary under one or more Bank Credit
                  Agreements to execute and deliver to the Trustee a
                  supplemental indenture pursuant to which such Domestic
                  Subsidiary or Restricted Subsidiary will Guarantee payment of
                  the Securities on the same terms and conditions as those set
                  forth in this Indenture. Each Subsidiary Guaranty will be
                  limited in amount to an amount not to exceed the maximum
                  amount that can be Guaranteed by the applicable Subsidiary
                  Guarantor without rendering such Subsidiary Guaranty voidable
                  under applicable law relating to fraudulent conveyance or
                  fraudulent transfer or similar laws affecting the rights of
                  creditors generally.

                  (c)      Section 11.6 of the Indenture is amended and restated
                  to read as follows:

                  SECTION 11.6. Release of Subsidiary Guarantor. A Subsidiary
                  Guarantor may, by execution and delivery to the Trustee of a
                  supplemental indenture satisfactory to the Trustee, be
                  released from its Guarantee either: (a) upon the sale of all
                  of its Capital Stock, or all or substantially all of the
                  assets of the applicable Subsidiary Guarantor, to any Person
                  that is not a Subsidiary of the Company, if such sale is made
                  in compliance with this Indenture or (b) upon the release of
                  (i) if such Subsidiary Guarantor is a Domestic Subsidiary, its
                  Obligations or Guarantees under all Bank Credit Agreements or
                  (ii) such Subsidiary Guarantor's Guarantee of the Obligations
                  of the Company or any of the Company's Domestic Subsidiaries
                  under all Bank Credit Agreements.

         3.       Removal of Subsidiary Guarantees.  In accordance with the
provisions of Section 11.5 and Section 11.6(b)(ii), as set forth above, of the
Indenture, each of BMG Holdings Inc., an Ontario corporation ("Holdings"), BMG
North America Limited, an Ontario corporation ("BMG"), and Oxford Suspension
Ltd., an Ontario corporation ("Suspension," and together with

<PAGE>   3

Holdings and BMG, the "Existing Canadian Subsidiaries") shall be released and
discharged from the terms and conditions of Article 11 of the Indenture and
shall no longer be considered to be Subsidiary Guarantors for purposes of the
Indenture. From and after the date hereof, each Existing Canadian Subsidiary
shall no longer be a Subsidiary Guarantor for all purposes under the Indenture
and the Securities.

         4.       Effective Time. The amendments to the Indenture set forth in
this Supplemental Indenture shall only become effective upon the execution and
delivery of this Supplemental Indenture by the Company, the Subsidiary
Guarantors, and the Trustee.

         5.       Ratification of Indenture; Supplemental Indentures Part of
Indenture. Except as expressly amended hereby, the Indenture is in all respects
ratified and confirmed and all the terms, conditions and provisions thereof
shall remain in full force and effect. This Supplemental Indenture shall form a
part of the Indenture for all purposes, and every holder of Securities
heretofore or hereafter authenticated and delivered shall be bound hereby.

         6.       Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED
BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK BUT
WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT
THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED
THEREBY.

         7.       Trustee Makes No Representation. The Trustee makes no
representation as to the validity or sufficiency of this Supplemental Indenture.

         8.       Counterparts. The parties may sign any number of copies of
this Supplemental Indenture.  Each signed copy shall be an original, but all of
them together represent the same agreement.

         9.       Effect of Headings. The Section headings herein are for
convenience only and shall not affect the construction thereof.

                      [This space intentionally left blank]

<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed as of the date first above written.

                         OXFORD AUTOMOTIVE, INC.

                         By:    /s/ Aurelian Bukatko
                                ------------------------------------------
                         Name:  Aurelian Bukatko
                         Title: Sr. Vice President-Chief Financial Officer

                         SUBSIDIARY GUARANTORS:

                         BMG NORTH AMERICA LIMITED
                         LOBDELL EMERY CORPORATION
                         WINCHESTER FABRICATION CORPORATION
                         CREATIVE FABRICATION CORPORATION
                         PARALLEL GROUP INTERNATIONAL, INC.
                         CONCEPT MANAGEMENT CORPORATION
                         LEWIS EMERY CAPITAL CORPORATION
                         BMG HOLDINGS, INC.
                         HOWELL INDUSTRIES, INC.
                         RPI HOLDINGS, INC.
                         RPI, INC.
                         PRUDENVILLE MANUFACTURING, INC.
                         OXFORD SUSPENSION, INC.
                         OXFORD SUSPENSION LTD.
                         OASP, INC.
                         OASP II, INC.
                         CE TECHNOLOGIES, INC.
                         TOOL AND ENGINEERING COMPANY

                         By:    /s/ Aurelian Bukatko
                                ------------------------------------------
                         Name:  Aurelian Bukatko
                         Title: Vice President-Chief Financial Officer

                         LASERWELD INTERNATIONAL, L.L.C.
                         By:  Lobdell Emery Corporation, its sole member

                         By:    /s/ Aurelian Bukatko
                                ------------------------------------------
                         Name:  Aurelian Bukatko
                         Title: Vice President-Chief Financial Officer

<PAGE>   5

                                     U.S. BANK TRUST NATIONAL ASSOCIATION, as
                                     Trustee

                                     By:    /s/ Michael T. Goodwin
                                            ------------------------------------
                                     Name:  Michael T. Goodwin
                                     Title: Assistant Vice President<PAGE>   1
                                                                     EXHIBIT 4.2

                             SUPPLEMENTAL INDENTURE

         SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of
August 29, 2000, among Oxford Automotive, Inc., a Michigan corporation (the
"Company"), the Subsidiary Guarantors (the "Subsidiary Guarantors") under the
Indenture referred to below, and U.S. Bank Trust National Association, a
national banking association, as trustee under the Indenture referred to below
(the "Trustee").

         WHEREAS the Company has heretofore executed and delivered to the
Trustee an Indenture (as such may be amended from time to time, the
"Indenture"), dated as of December 1, 1998, providing for the issuance of an
aggregate principal amount of $250,000,000 of 10 1/8% Senior Subordinated Notes
Due 2007 (the "Securities");

         WHEREAS pursuant to Section 9.2 of the Indenture, the Trustee, the
Company and the Subsidiary Guarantors may, with the consent of the Holders (as
defined in the Indenture) of at least a majority in principal amount of the
Securities outstanding, execute and deliver this Supplemental Indenture for the
purpose of amending, modifying or changing certain provisions of the Indenture;

         WHEREAS the Company and the Subsidiary Guarantors desire to amend or
eliminate certain provisions of the Indenture as hereinafter set forth; and

         WHEREAS all acts and things necessary to amend the Indenture as
described above and to make this Supplemental Indenture a valid agreement of the
Company and the Subsidiary Guarantors, in accordance with its terms, have been
completed.

         NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Company, the Subsidiary Guarantors and the Trustee mutually covenant and agree
for the equal and ratable benefit of the Holders of the Securities as follows:

         1. Definitions.

            (a) Capitalized terms used herein without definition shall have the
meanings assigned to them in the Indenture.

            (b) For all purposes of this Supplemental Indenture, except as
otherwise herein expressly provided or unless the context otherwise requires:
(i) the terms and expressions used herein shall have the same meanings as
corresponding terms and expressions used in the Indenture; and (ii) the words
"herein," "hereof" and "hereby" and other words of similar import used in this
Supplemental Indenture refer to this Supplemental Indenture as a whole and not
to any particular section hereof.

<PAGE>   2

         2. Amendment to Indenture. The following sections of the Indenture are
modified as follows:

            (a) The following definition is hereby added to Section 1.1 of
the Indenture:

            "Domestic Subsidiary" means any Restricted Subsidiary of the
            Company organized under the laws of any state of the United
            States of America or the District of Columbia.

            (b) Section 4.14 of the Indenture is amended and restated to read as
follows:

            SECTION 4.14. Future Guarantors. The Company shall cause (a) each
            Domestic Subsidiary that at any time becomes an obligor or guarantor
            with respect to any Obligations under one or more Bank Credit
            Agreements and (b) each other Restricted Subsidiary that guarantees
            the Obligations of the Company or any Domestic Subsidiary under one
            or more Bank Credit Agreements to execute and deliver to the Trustee
            a supplemental indenture pursuant to which such Domestic Subsidiary
            or Restricted Subsidiary will Guarantee payment of the Securities on
            the same terms and conditions as those set forth in this Indenture.
            Each Subsidiary Guaranty will be limited in amount to an amount not
            to exceed the maximum amount that can be Guaranteed by the
            applicable Subsidiary Guarantor without rendering such Subsidiary
            Guaranty voidable under applicable law relating to fraudulent
            conveyance or fraudulent transfer or similar laws affecting the
            rights of creditors generally.

            (c) Section 11.6 of the Indenture is amended and restated to read as
follows:

            SECTION 11.6. Release of Subsidiary Guarantor. A Subsidiary
            Guarantor may, by execution and delivery to the Trustee of a
            supplemental indenture satisfactory to the Trustee, be released from
            its Guarantee either: (a) upon the sale of all of its Capital Stock,
            or all or substantially all of the assets of the applicable
            Subsidiary Guarantor, to any Person that is not a Subsidiary of the
            Company, if such sale is made in compliance with this Indenture or
            (b) upon the release of (i) if such Subsidiary Guarantor is a
            Domestic Subsidiary, its Obligations or Guarantees under all Bank
            Credit Agreements or (ii) such Subsidiary Guarantor's Guarantee of
            the Obligations of the Company or any of the Company's Domestic
            Subsidiaries under all Bank Credit Agreements.

         3. Removal of Subsidiary Guarantees. In accordance with the provisions
of Section 11.5 and Section 11.6(b)(ii), as set forth above, of the Indenture,
each of BMG Holdings Inc., an Ontario corporation ("Holdings"), BMG North
America Limited, an Ontario corporation ("BMG"), and Oxford Suspension Ltd., an
Ontario corporation ("Suspension," and together with

<PAGE>   3

Holdings and BMG, the "Existing Canadian Subsidiaries") shall be released and
discharged from the terms and conditions of Article 11 of the Indenture and
shall no longer be considered to be Subsidiary Guarantors for purposes of the
Indenture. From and after the date hereof, each Existing Canadian Subsidiary
shall no longer be a Subsidiary Guarantor for all purposes under the Indenture
and the Securities.

         4. Effective Time. The amendments to the Indenture set forth in this
Supplemental Indenture shall only become effective upon the execution and
delivery of this Supplemental Indenture by the Company, the Subsidiary
Guarantors, and the Trustee.

         5. Ratification of Indenture; Supplemental Indentures Part of
Indenture. Except as expressly amended hereby, the Indenture is in all respects
ratified and confirmed and all the terms, conditions and provisions thereof
shall remain in full force and effect. This Supplemental Indenture shall form a
part of the Indenture for all purposes, and every holder of Securities
heretofore or hereafter authenticated and delivered shall be bound hereby.

         6. Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT
GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT
THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

         7. Trustee Makes No Representation. The Trustee makes no representation
as to the validity or sufficiency of this Supplemental Indenture.

         8. Counterparts. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

         9. Effect of Headings. The Section headings herein are for convenience
only and shall not affect the construction thereof.

                      [This space intentionally left blank]

<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed as of the date first above written.

                                          OXFORD AUTOMOTIVE, INC.

                                          By:   /s/ Aurelian Bukatko
                                              --------------------------------
                                          Name: Aurelian Bukatko
                                          Title: Sr. Vice President-Chief
                                                 Financial Officer

                                          SUBSIDIARY GUARANTORS:

                                          BMG NORTH AMERICA LIMITED
                                          LOBDELL EMERY CORPORATION
                                          WINCHESTER FABRICATION CORPORATION
                                          CREATIVE FABRICATION CORPORATION
                                          PARALLEL GROUP INTERNATIONAL, INC.
                                          CONCEPT MANAGEMENT CORPORATION
                                          LEWIS EMERY CAPITAL CORPORATION
                                          BMG HOLDINGS, INC.
                                          HOWELL INDUSTRIES, INC.
                                          RPI HOLDINGS, INC.
                                          RPI, INC.
                                          PRUDENVILLE MANUFACTURING, INC.
                                          OXFORD SUSPENSION, INC.
                                          OXFORD SUSPENSION LTD.
                                          OASP, INC.
                                          OASP II, INC.
                                          CE TECHNOLOGIES, INC.
                                          TOOL AND ENGINEERING COMPANY

                                          By:     /s/ Aurelian Bukatko
                                              --------------------------------
                                          Name: Aurelian Bukatko
                                          Title: Vice President-Chief
                                                 Financial Officer

                                          LASERWELD INTERNATIONAL, L.L.C.
                                          By:  Lobdell Emery Corporation, its
                                               sole member

                                          By:    /s/ Aurelian Bukatko
                                              --------------------------------
                                          Name: Aurelian Bukatko
                                          Title: Vice President-Chief
                                                 Financial Officer

<PAGE>   5

                                          U.S. BANK TRUST NATIONAL ASSOCIATION,
                                          as Trustee

                                          By:    /s/ Michael T. Goodwin
                                             ---------------------------------
                                             Name: Michael T. Goodwin
                                             Title: Assistant Vice President

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