Regarding your 4th question about the rear end clunk, it could be a worn out flex plate.
These cars have a driveline that has flexible rubber discs at both ends, and a center U-joint with a support bearing. The front usually wears out, and should be examined anyway considering the car has 120,000 miles.
Your differential mounts could also be broken.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".