I too have the same situation on a 2007 model.
I complained to my Mercedes loving friend today and he said a mouth full.
"You buy a BMW for PERFORMANCE NOT RELIABILITY!!!!"
Dang I thought, he is so right. These things drive like a bat out of hell and break like an old lady.
I had not thought about the film but did consider caulking the crack with black silicon and disconnecting the power switch. The dealer and a sport shop wanted $3000 to replace all the cassettes. They don't seem to want to replace individual parts. I believe this is because the labor to get all the interior out is 10 hours. If I were repairing it myself and spent that much time on it, I would put all new parts in since they are made of plastic and fiberglass crap that don't last. Just imagine spending the weekend pulling the interior out and rebuilding the roof and putting it all back together just to have another part break or the new ones break prematurely because the tracks were worn or cracked etc etc.
My car mildewed in the carpet front and back on passenger side. I treated it with a no chlorine mildew killer and it smells no better. So I checked on the carpet/pad kits for front and back. $1500. DANG! So if I do it myself it will cost about $3000 to fix this car and if I pay someone it will cost about $5000.
My wife will not even ride in it it smells so bad.
I hate BMW.
Buy a Lexus, Accura, Infinity ....