My 2008 Audi A6 has a sunroof that will pop up or retract. Recently I had it popped up and tried to lower it, only to hear a pop and see a piece of black plastic fall to the floorboard. The sunroof would not completely lower until I noticed a plastic support arm on the driver's side of the sunroof appeared to be broken. I was able to push it back into place and completely lower the sunroof, but now I'm afraid to pop it up again. This morning I retracted the sunroof and heard more loud pops, so I immediately closed it. Any ideas on what has broken and how much it will cost to fix?