My friend has a 1997 E420 with 145,000 on it. He had the transmission fluid & filter changed and within 2 weeks the tranny started slipping. The mechanic did not change the torque convertor fluid. It did not slip before. The replacement fluid was the expensive M/B fluid for the 722.6 transmission.

Did the mechanic cause the tranny to start slipping because he did or didn't do something he should have? Any opinions would help.