I can't nail it down without the part number off the computer i question but here are some spots for you to check:

1) you could try Phil from Fastlane, the guy who hosts this site, by clicking buy parts above and giving him a call.

2) http://motors.shop.ebay.com/Engine-Computers-/33596/i.html?_dmpt=Motors_Car_Truck_Parts_Accessories&_fln=1&_mqf=0&_qfkw=1&_trksid=p4506.c0.m273&_myi=1992&Make=Mercedes%252DBenz&Model=300D

3) http://www.mercedesbenzautocomputers.com/index.php

4) http://www.acdelcocomputers.com/computers/Mercedes-Benz.htm

good luck

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1972 280SE 4.5