Mine is doing the same thing, it looks really ugly. Its a common problems on bmws i believe, my friend with a 3 series has the same prob. Should be able to just replace the glass im guessing and keep the original housing.

I just looked it up on realoem, it realls depends on if you have auto dimming or not, if you do its a lot more.

Without (Drivers):
51168408797 $77.84



With (Drivers)
51168247769 $266.72