I love the M104, I have a 97 C280 and it is very reliable.
Just two possibilities to look out for, which have been discussed numerous times here: the possibility of an oil leak at the headgasket and the wiring harness.
I would definitely recommend the C280.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record