[Brando]

Fact: You knew it was broken before taking it there.
Fact: They opened the sun roof, but didn't know any better.

So: The Midas shop didn't break it.

Should they have closed it? Maybe. Or at least, known how to. Most definitely they shouldn't have given you the chatter run-around about "it was open when we got it", etc. Lying I cannot tolerate and calling them on their BS is prime.

IMHO you should have informed them it was broken and they shouldn't have to pay half the bill for a repair that they're not responsible for.

I've been in a similar situation before at previous employment. Customer forgets to tell you that something non-critical was inoperable, and we took the courtesy to inform them. Sadly, you always get one or two that pretend that it worked before, but you broke it. Those are fun.