Yeah, good advice!
I have a 1992 300SD with 200K on it. For my little experience and, most, for what I read on the different forums on the net, any car with this age (or more) and mileage may have problems. Still, the 300SD is a great car, full of comfort and style. And top safety.
Whoever says that you have to avoid it, is because probably he doesn't know it. You can buy a 1991 300SD and have the double of problems you may have with a 1992 300SD.
Good luck.