I'm picking up my E39 M5 today. It has a small area of bubbling paint on the rear bumper as well as a poorly repaired rust patch near the filler cap. I'll take some pictures and add them to the thread once I've got the car but I thought I'd start the ball rolling now.
The filler cap area is my biggest concern: the previous owner says that water collected just inside the filler cap and a rust patch formed. The area has been filled and repainted so I can't see what's underneath. It's a very small area so I'm hoping that it can be properly fixed.