This thread isn't about an official BMW replacement part but you may want to check here for a cheap alternative:
http://www.318ti.org/forum/showthread.php?t=13422 My brother is looking into doing this fix shortly on his TI.
The official BMW part # can be found here:
http://www.realoem.com/bmw/showparts...60&hg=41&fg=60 You may just want to go to realoem.com a do a search on your specific make and model, as I just plugged mine in. Good Luck.