Wiring Harness - Yes. Headgasket - Yes.

Transmission wear is number of shifts not miles. City driving wears the tranny faster than highway mileage. Other thing is whether the transmission
fluid and transmission filter was changed regularly . I do it every 30,000 miles, but I suppose 60,000 would work. I have no stats, but seems to me
that these transmissions are very robust.

Maintenance expenses? That number would all over the board. It is not the regular things like Oil and Filter, Air Cleaner, etc. It's the other things that
can be expensive when they go bad. A/C Compressor, Alternator, Air Pump, Belt Tensioner, Water Pump. The cost of parts is not outrageous. You do want to try to do most of the work yourself, or alternatively, find a good honest independent shop that specializes in these cars.

Do not try to buy the cheapest example out there. As the saying goes, "There's nothing more expensive than a cheap Mercedes".

Steve

I used to have an 89 325is, so I'm aware of the cost of German cars.

I do much of my own work, and the 325 was easy to work on.

Thanks for all the tips, and keep em coming if you got em.