1997 AND 1998 model year 722.6 trannies have some problems, but despite so many out there, as a percentage it's surprisingly low.
The 97's have an updated valve body for some applications (I understand the SLK is the prime culprit here) and others have the control module changed.
I talked to a very knowledgable tech this week that talked about seeing a few 1998 722.6's with a failing temp sensor that would throw the car into limp home mode. The "other" shop would dissconnect the wiring/sensors, and rebuild the tranny. Problem NOT solved.
As to the 1997 M104 engines, I know one 1997 C280 with low miles and a leaking gasket, and one 1997 E320 with ridiculous miles and not one single leak. Luck of the draw?
1998 C230 "Black Betty"