Herb has it right, we have seen a lot more of this of late. As these cars have dropped in price and people are picking them up they are finding the pitfalls of German Engineering and high end vehicles.
Holding your mechanic accountable is easy to say but hard to do. They have the upper hand, if you get your car home and it starts leaking again they can just say it is another gasket and you had 2 problems. Believe me I know. You can never go there again, but to make them repair the second one and rebate you the misdiagnosed original cost is virtually impossible. It all depends on the owner I suppose.
I feel for the OP, but the statement about a Lemon Law struck me the most. On a 7 year old car?