My diesel '99 e300 had 370k before the diff was replaced because it was skipping. My other '98 e300 i sold a few months ago had 350k on it and the gears were in great condition when I resealed it. The older diffs are just as solid. Differentials aren't hard to rebuild anyway comes to situation..

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k