The M104 engine in the car you are looking at has some problems relating to the head gasket as well as the previously mentioned wiring harness. Make sure that the engine is not seeping any oil or coolant from the cylinder head gasket and that the coolant has no oil mixed in with it. Beyond those problems, the M104 is a pretty stout unit, and with proper care and attention it will last for many more miles. There are of course problems with the ASR traction control so I would make sure that the system works as it should with no warning lights or that it does not go into 'limp' mode with symptoms of the throttle control being greatly reduced. I would avoid a car with ASR if I could as problems with it are often a nuisance to fix and costly.

Other coupe particulars to pay attention to are the seatbelt retractors. Make sure that they extend and retract as they should when you turn the car on or close a door with the ignition on. The front seat backs should lock into place when the engine is running and the doors are closed. They are not locked when the engine is off or the corresponding front door is opened. Ensure that all the electric accessories work, and that the climate control system is up to par. A good pre purchase inspection should reveal any other faults about the particular car you are looking at.

On a final note, you can't go wrong with the style of the classic pillarless coupes, and they are rare compared to other W124 models. It is not that often that I see another example roaming the roads. Good luck with your purchase!