the wiring harness isuue only affects late 1992 -1995 m104's from what I know.
Other than that, head gasket is the only other issue I know about.
Haven't heard of any leaking elsewhere.
Mines at 103k no leaks, no harness problems. My car was made aug 1991 though, but is a 92 model year.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.