I just had the wiring harness replaced on the E320 and MB picked up the cost of the part. I paid the labor. I think I was told there is a national MB warranty for the harness. If you have the Starmark it might cover it regardless. I also had the head gasket replaced and there was noticeable oil leakage coming from the right front corner of the head. That was after the front cover had been resealed. Do both and you have accomplished repairing what I am told are the two most common 104 problems. Good luck.
BTW, the car had 106,000 miles on it when this work was done.

Redflash

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1997 S600 Coupe
2002 Lexus SC430
2004 Lexus RX330 (wife's car)
Owned:
1993 500 SEL
1994 E320 (wife's car)
1987 300 SDL
1978 450 SEL
1980 300 TD (wife's car)
1969 280 SL