well my car had just gone out of warranty and I had got exactly the same problem as yours. I took it to the dealer and was all prepared to fight with BMW, as this a pre-mature failure of the part. BMW's are not made for 3 to 4 years!! c'mon this cars are good upto 200,000 miles.
But BMW is great and they are fixing it for me at their cost.. so I am a happy camper!
You never lose by asking!
Try your luck..