Considering buying a C240 2.6L, AWD.whats to good and bad?

Besides the obvious stuff (oil leaks, service records, body damage, etc.) check to make sure the notorious Valeo radiator has been replaced. It was known to let coolant and transmission fluid mix and thus kill the transmission.

Refer to this:

Identification of the early Valeo Radiator? - Mercedes-Benz Owners' Forums

The attached images show the TSB's identifing the Valeo as being bad along with visual identification cues.

Don, MBZ's "$Matic" system is pretty much bulletproof. It uses tried-and-trusted open differentials and the ABS/ESP system to regulate wheelspin. It works very well with minimal extra components. About the most serious problem I ever hear reported is some irregular brake pad wear, but that's it.