The 95 S class has a DIN size radio, the 98-99 ML also is a DIN size. 2000 and new MSC units are double-DIN size, so if you have a 2000 or newer ML, it would need an adapter of some sort to fit the S class radio, usually a DIN-sized storage box is used in factory applications.
I think it would fit OK into a 98-99, but I'm afraid the wiring would be too different to make it a worthwhile swap (not worth the effort IMO).

Gilly