I would say that you are correct, the car wash did it. Which doesn't make you feel any better, or your X look any better. I have a friend in Minnesota that owns a gas station/ car wash, and having helped him work on it, I can tell you that if the owner of your car wash isn't keeping up on his filter maintenance, then lots of dirty water is getting cycled thru.

I can't think of any good options to persue, other than make a really huge stink about it. Or make friends with a lawyer. Or a hit man.