The common issue with M104's is failed head gaskets. It seems to occur somewhere between 100-150,000 miles judging by reports and engine wiring looms can start to break up, the insulation starts to degrade and bare wires touch! First signs can be a mis-fire. All 717 manual gearboxes should bolt up, even a Getrag from a 190E 2.3/2.5-16 from what I recall. The C280 M104 was available from the factory with a 717.441 manual transmission.