I believe the decreasing quality rumors are nothing but myth and urban legend. I've owned 124 and 210 cars. They are both great. I've been hearing the "they don't make the Benz as good as that last model" stuff since the 123 cars came out, that's almost 25 years ago.

If it were me, and I had the money, I'd take the 210 turbodiesel in a heartbeat. This is the last of the Benz diesels in the US for probably a long time, or maybe forever. They are great cars and take no more preventive maintenance than any other.

There is not such thing as a "tune up" on a diesel. Actually there is no such thing as a tune up on any car any more. The preventive maintenance is really not much more than keeping up with changing fluids and filters as prescribed by the maintenance schedule.

Good luck and enjoy,