I'm not sure what to think of you mechanic. It must be nice to gain experience at others expense.
Yes, This may be a bit harsh but, I used to be in the service industry myself and there's NO way I would have charged a customer for the "shotgun" approach of changing parts.
I believe I would have to discuss the $622 bill.
Perhaps he will include you on future MB repairs. You are entitled to a "cut" in my opinion.
Glad your running again. Good luck.