Agree with Steve, not a rear end problem. Likely worn flex disks or differential mounts causing the clunk.
Rolling about 1-6-10 inches when placed in park is normal. That is the distance it takes the parking pawl to engage the notch in the transmission. Not sure when they beefed up the pawl, it's real beefy on the 126, but on the 108 I always, always, always use the hand brake, because it doesn't always engage.
The delay in engaging reverse has nothing to do with the differential, that's in the tranny. Most folks I know just live with it. So you have to wait a couple seconds, no biggie.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.