I've had a few 190E's in the family, and have found them pretty reliable cars, but they do have their problems. One problem can be a mechanic not intimate with MB cars. These things are not "most" cars.
(Seen those ads? $39.95 muffler, most cars)
You need to take the car back, and see if he can repair it properly without charging you your last remaining arm and leg. And no matter the outcome, start asking about for some leads on someone that won't give you back a broken car. My indie mechanic test-drives cars to ensure they are working properly before returning them.
I don't have an answer for you concerning this particular problem. I do wonder if OVP was a problem back in '85? Hhhmmm...
1998 C230 "Black Betty"