If there's a piece of the bolt stuck in the crank, then you've got a lot of work to do, but if the dealer knew about it and tried to cover it up by continually tightening it up, at least you know who's directly to blame for it. Even though it won't do you any good, I'd confront them with your findings. Personally, I love getting into yelling matches with service managers over thier "antics". I would make a hobby out of it if I could.