The best time to address this issue is at the time of the repair. If the repair is done correctly then the value is not diminished. In my state we can pick the shop that does the repair. I would require the work be done at the shop that does all the work for the dealer and specializes in Mercedes and BMW. At this point the car has been fixed so you are stuck with whatever you have, excepting any defects that are covered by any kind of guarantee. Of course keeping in mind that the people fixing any defect will be the ones who caused the defect...

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra