I had this same problem and I think its specific to 85's. Never fixed mine, put a stick in. Guy I sold my auto to put it in an 83 and never had a problem with it.

Verify speedo based on gps.

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42