His mechanic diagnosed it as a bad injector on #2 and on the surface thats what it seems like. Crack #2 and it goes away. We replaced the injector and the knock is still there. When I pulled the injector and replace the head shield there was a metal cup underneath, unlike my 300D. Is this normal? Any idea what it might be?

Car is beautiful with under 100k on it.

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42