<PAGE>

                                                                 EXHIBIT 10.3


         Extension and Fifth Amendment of Lease, dated as of February 23, 2000,
by and between RTC PROPERTIES, Inc, a New York corporation having an office at
79 Fifth Avenue, Suite 1800, New York, New York 10003 ("Lessor"), and BURKE
INDUSTRIES, INC. (as assignee in interest of MERCER PRODUCTS CO., INC.), a
California corporation having an office at Building 10, Hackensack Avenue, Port
Kearny, South Kearny, New Jersey 07032 ("Lessee").

                                   WITNESSETH:

         WHEREAS, Lessor, as lessor, and Lessee, as lessee, entered into a lease
dated as of December 1, 1988, as amended by an Extension and First Amendment of
Lease dated as of January 13, 1994, an Extension and Second Amendment of Lease
dated as of January 23, 1995, a Third Amendment and Extension of Agreement of
Lease dated as of March 1997 and by a Fourth Amendment of Lease dated as of
April 21, 1998 (as amended, the "Lease") of certain premises including a portion
of Building 10 identified as 10C (formerly identified as 10B), as more
particularly described therein (the "Premises");

         WHEREAS, Lessor and Lessee desire to extend the Lease for an additional
term of five (5) years;

         WHEREAS, coincident and said extension, Lessor and Lessee desire to
amend certain provisions of the Lease relating to security of Lessee's
performance and obligations under the Lease and to amend certain other
provisions of the Lease;

         NOW, THEREFORE, Lessor and Lessee do hereby amend the Lease as follows:

         PARAGRAPH 1. Effective immediately, Section 1.01 of the Lease is hereby
amended by deleting all references to the Expiration Date "April 30, 2000" and
inserting the date "April 30, 2005" in its place and stead.

         PARAGRAPH 2. Effective immediately, Section 2.01.A. of the Lease shall
be deemed amended by deleting all references to the phrase "Expiration Date" and
inserting the phrase "April 30, 2000" in its place and stead.

         PARAGRAPH 3. Effective May 1, 2000, the following shall be deemed
inserted after Section 2.01.A. of the Lease:

         "Section 2.01.B. Lessee shall pay to Lessor, or such other person as
         Lessor may from time to time designate, at an address specified in or
         pursuant to Section 2.03, during the Term, fixed rent ("Fixed Rent"),
         over and above the other and additional payments to be made by Lessee
         as hereafter provided, of One Hundred Sixty Two Thousand Five Hundred
         ($162,500.00) Dollars per annum for the period from May 1, 2000 through
         the Expiration Date, payable in advance in equal monthly installments
         of Thirteen Thousand Five Hundred Forty One and 67/xx ($13,541.67)
         Dollars each on the first day of each and every month during such said
         period."

         PARAGRAPH 4. Effective May 1, 2000, the following shall be deemed
inserted following Section 32.03 of the Lease:

<PAGE>

         "Section 32.04. In addition to the security deposited with Lessor by
         Lessee under Section 32.01, additional security in the sum of
         $18,625.00 shall be deposited with Lessor (and maintained throughout
         the Term) by Lessee for the faithful performance and observance by
         Lessee of the terms, covenants and conditions of this Lease including
         the payment of any Fixed Rent and Additional Rent. Said additional
         security shall be in the form of cash or a clean, irrevocable bank
         letter of credit reasonably acceptable to Lessor in all respects and
         providing that Lessor may draw upon it at any time and from time to
         time in its sole discretion when Lessee is in default in observing or
         performing its obligations under this Lease. Said letter of credit, by
         its terms, shall be automatically extended for periods of one year from
         the present or any future expiration date thereof, it being the
         intention of Lessor and Lessee that at all times during the Term and
         the period of sixty (60) days thereafter Lessor shall be in possession
         of a letter of credit representing said additional security in the
         amount of $18,625.00, acceptable, as aforesaid, or the sum of
         $18,625.00. If Lessee performs all of Lessee's obligations hereunder
         the Lease, said additional security deposit, or so much thereof as has
         not theretofore been applied by Lessor, shall be returned to Lessee at
         the expiration of the Term hereof, and after Lessee has vacated the
         Premises.

         Section 32.05. Any cash security deposit provided by Lessee to Lessor
         under Section 32.04 shall be deposited by Lessor with a banking
         institution in an interest-bearing savings account or certificate of
         deposit or similar instrument within a reasonable time after receipt of
         such deposit by Lessor. Upon demand of Lessee (made no more frequently
         than once in each calendar year), Lessor shall pay to Lessee the
         interest then held in such savings account or accrued with respect to
         such certificate of deposit or other instrument (to the extent payable
         by the particular financial institution) as the case may be, provided
         that Lessor shall not be obligated to make any such payment if the
         additional security, provided by Lessee under Section 32.04, held by it
         hereunder would thereby be reduced below the sum of $18,625.00. Lessor
         shall have no duty to obtain any particular rate of interest and no
         liability for any loss in connection with the deposit."

         PARAGRAPH 5. Promptly upon execution and delivery of this Extension
and Fifth Amendment of Lease by Lessor and Lessee, Lessor shall proceed
diligently (subject to Unavoidable Delays) and in a good and workmanlike
manner to complete the item of work set forth in that certain work letter
between Lessor and Lessee dated as of even date herewith.

         PARAGRAPH 6. There shall be no further privilege of extension of this
Lease beyond this extension of the Terms.

         PARAGRAPH 7. Unless otherwise expressly provided herein, initially
capitalized terms used herein shall have the same meaning that they have in
the Lease.

         PARAGRAPH 8. Except as modified herein, the provisions of the Lease
shall continue in full force and effect.

         IN WITNESS WHEREOF, Lessor and Lessee have duly executed this
Extension and Fifth Amendment of Lease as of the day and year first above
written.

                                      2

<PAGE>

                                       RTC PROPERTIES, INC.


                                       By:  /s/ John L. Neu
                                            ----------------------------

ATTEST:                                BURKE INDUSTRIES, INC.


By:  /s/ Elliot Stein                  By:  /s/ Stephen G. Geane
     ----------------                       --------------------

                                       3

<PAGE>

                             As of February 23, 2000

RTC Properties, Inc.
79 Fifth Avenue
Suite 1800
New York, NY  10003



                     Re: WORK LETTER: BUILDING 10, UNIT 10C


Gentlemen:

         Reference is made to the Agreement of Lease dated as of December 1,
1998, as amended by an Extension and First Amendment of Lease dated as of
January 13, 1994; an Extension and Second Amendment of Lease dated as of
January 25, 1995; a Third Amendment and Extension of Agreement of Lease,
dated as of March 1997; a Fourth Amendment of Lease dated as of April 21,
1998, and by an Extension and Fifth Amendment of Lease dated as of even date
herewith (as amended, the "Lease"), between RTC Properties, Inc., as lessor
("Lessor"), and Burke Industries, Inc., as lessee ("Lessee"), covering
premises described therein (the "Premises"). (Terms used herein which are
defined in the Lease shall have the meanings respectively attributed in the
Lease, unless otherwise provided herein.)

         This letter will confirm Lessor's agreement to perform the following
item of work (the "Work") at the Premises:

ITEM NO.

1.       INSTALL NEW FLOORING IN ENTRANCEWAY OF PREMISES.

         Lessor shall supply labor for the Work at its sole cost and expense.
All materials for the Work shall be supplied by Lessor at Lessee's sole cost
and expense and shall be billed by Lessor to Lessee as Additional Rent.
Lessor shall proceed diligently to substantially complete the Work subject to
Unavoidable Delays; however, the time of completion of the Work shall not
affect Lessee's obligations under the Lease. All Work shall be performed to
building standard or equal quality, in a good workmanlike manner. Lessor's
obligation to perform the Work shall be a single, non-recurring duty; upon
performance of an item of Work, Lessor shall no longer have any duty to
perform the same or any similar item of Work, nor shall Lessor have any duty
to perform repair or maintenance with respect thereto. The inclusion of any
particular item herein is not intended to modify the respective repair
obligations of the parties set forth in the Lease. For the purposes of
Article Ninth of the Lease, the Work shall be deemed to be work performed
pursuant to the Lease. The provisions of Section 25.02 of the Lease shall be
applicable to the Work. Lessee shall use and occupy the Premises in such
manner as shall not cause interference with the performance of any Work.

<PAGE>

         Kindly indicate your agreement to the foregoing by signing a copy
hereof and return it to us.

                                                     Very truly yours,

                                                     BURKE INDUSTRIES, INC.


                                                     By: /s/ Stephen G. Geane
                                                         --------------------
Agreed:

RTC. PROPERTIES


By:  /s/ John L. Neu
     ---------------------------

                                       5