There are 2 kinds of drain plugs for the V8 engines. Mine have the type with a very soft aluminium washer that can damage easily when putting them back in. They are cheap and I think worth replacing every time.

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1993 190E 2.0L (Euro.) sold
1991. 500 SEL (Euro.)
1991. 300 CE (Euro.) sold
1993. 500 E (U.S. spec.)