93 300E rear clunk sound

[georges]

Hello everyone. Having read this forum with great admiration for quite some time it is finally time to join in the membership.
I need advice with my 93 2.8 300E.
It has 160,000 miles, we've owned it for about the last 30K (2 years) almost all long distance freeway driving. Never a problem.
We love this car but it has developped a very annoying/frightening problem in a clunking sound coming from the right rear wheel area.
It happens only when I start out from a stop and not all the time.
It will clunk in time with the wheel revolutions.
I have read a lot of the posts concerning this type of problem, removed the rear wheels, inspected as well as I could, the only thing I find strange is the half shafts move in and out about 1" (from boot to boot)
The right rear wheel can be rotated just a little, enough to emit a clunking sound from the drive line.
The flex discs seem ok.
The rubber boots are all fine.
The sway links are fine.
The shocks and boots are fine.
Thank you for any advice or ideas.