3 differences come to mind. They only come to mind because of my recent acquistion, '97 S320. I have been trying to learn as much as possible about the W140.

Wiring Harness - One of our Forum members pointed out today that '97 was the first year of the non-disintegrating wire harnesses at least on the S320's.

Belt tensioner is revised. Much simpler designer. Longevity? Can't be worse the original design.

The M104 in the S320 is totally uncluttered in the large engine compartment.
I think that means a slightly cooler environent.

Head Gasket? Can only say that mine had a head gasket done at 67K miles.

While, not an engine difference, the transmission is the 722.6 in the S320 starting I think in '96.

From all I have read and heard, the M104 will run a very long time given proper fluid and filter changes. My M103 in my '92 300E is running strong at
244K miles.

Do a search on S320 to see the several other threads on the subject.

Steve
'97 S320 108K
'92 300E Sportline 244K