Well, the shop didn't see anything wrong with the wiring, but I decided to take a look myself. When I took the liner off the trunk lid, I found a wire from the emergency release button was dented where it contacted the sharp edge of the trunk lid, right where the wires were tightly fastened to the lid with a zip tie. I cut the tie and put some electrical tape on the damaged wire, and we haven't had a problem in 3 days. I sure hope it's fixed now. Thanks for the advice. I found a post on BenzWorld describing the same thing, and one of the replies said there was a TSB on this. I guess the MB dealer didn't get that one...