I think this has been a very good thread from start to finish and it would be great to hear the rest of the story when you identify the remaining issue. Finding loose nuts on the ujoints brings to mind a practice that I find helpful on critical components is to "mark" each fastener after tightening / torgueing with a paint marker. I use green or yellow. It helps me to make sure that I've did each fastener and because I make a "line" across the head or nut to the attached surface I can see if it's "moved" or came loose later.
