I used Auto Windscreens and managed to get a Genuine BMW part.
Although they said a non Gen one would also be its replacment, I just simply put in a request for a Genuine BMW part and without a fight it got approved. I see no issue with yours should you ask, however it all depends on your Insurance Company as they're the ones to be paying Auto Windscreens for the work.
Call Auto Windscreens and they will deal with the request and will liaise with your Insurance Co.
As G-Dog mentioned, both Pilkington and BMWs part is identical - bar the small BMW logo printed above the word 'Pilkington'. Its either applied during manufacture or added after.
More info:
http://www.cslregister.com/forum/showthread.php?t=10931