These are really nice cars, but there are some achilles heels.
To begin with, this car has the two cam, inline six M104 engine. It runs great, but does have a history of head gasket problems. The odds are in your favor that it will not give trouble, but if it does, you are looking at $1,500 or more to have this work done. If you can do it yourself, you should do a valve job at the same time and it would probably cost $500 to $800.
Secondly, there is a problem with the earlier a/c evaporators. I don't know if this applies to the later cars.
That said, the 124 series MB is one of the greatest MB cars ever made IMHO. The cars are great to drive and generally hold up extremely well.