I hate to be so jaded, but I don't trust your mechanic. Did you find the parts in the pan or did he claim to find them and told and showed them to you? Also with your problem, he's trying to replace your brake master cylinder? Maybe it's bad, but obviously not related to the main problem. When I first saw the thread I thought of spark plugs, coils, and injectors. Getting the engine replaced would be my last resort. I'd get a fresh set of eyes on the problem if I were you.