With out knowing what is causing the stain it's pretty hard to suggest how to clean it. I guess the one piece of advise I could give is never let the dealer (or anyone else for that matter) wash your car. I'm the only one that washes my cars so that way if something happens I only have myself to blame.
Hope they can help you out and either clean up their mess or replace your covers.
Hope they can help you out and either clean up their mess or replace your covers.