Dropped Engine
You have to look at it from the shops view, the bolt broke and unless it you could see that it was in bad shape then it really is just bad luck, there is nothing they could have done to prevent it from happening but I do agree that since it happened under their care they should at LEAST check the parts and gaskets for free and offer a discount for the build. I would ask for them to pay for the parts as well though just because the worst they can do is say no.