I have a 1997 (W210) E420 and it has the 2.82 diff.
I have often thought, what a shame it does not have the E320 3.07 differential but I do not know if that would work.
You might want to check if the 1997 2.82 diff would fit into the w124 E420.

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2008 S550
2010 GLK350
1997 E420 (retired)
2005 CLK500 (retired)