My car is going back to MB private repair shop for a third time to replace the 772.6 tranmission wiring harness connector part. Ihe new parts are starting to leak after 40-50 miles of use. Has anyone else had this problem? I am told the new part is defective. Their service warranty has covered the labor and part so far.

I'm assuming you are talking about the plastic bushing piece where harness attaches to transmission. Yes, that should get replaced every transmission service 50 to 60k miles.

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Jim