Wow!! I third this one!!!!!
Now at 80K; have had this exact issue since approx 65K, and then it got too damn cold outside for me to address it! I think it may be the differential mounts, but it is a bit odd that it happens only once (or twice) a day, just after that initial "cold" reverse and then the shift to drive. Clunk. You'd think that if it was the mounts, it would happen all the time!
I drove a 190E last year that did the same thing, too!
Brian

__________________
Brian
1995 E320 wagon