how are your engine/tranny mounts? all in good shape?
Couldn't a bad mount cause extra movement when accelerating etc of the tranny etc?
At the cost of the flex discs, the rear shouldn't be a big deal to change regardless.
I had both of mine done due to slight cracking in them, not that I notice a difference, but it gives me peace of mind knowing I can track their mileage now..
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.