I just had the Center Bearign and Flex Disk replaced in my 1994 740iL. The mechanic never test drove it afterward - if he di he would have noticed that the thumping sound of the driveshaft against the body was still there. I agee that it seemed reasonable to assume tha the driveshaft would have fixed it, but....
Anyway, the center bearing went again, and the new mechanic found that the thumping still hasn't gone away. They had the driveshaft tested, and it spum fine. Now I'm worried that it might be related to the tranny - it has had a problem shiting into reverse when warm, and there may be a low level vibration when in 3rd gear. Has anyone ran into this?