I have put some RainX on there in the past, but to be honest if I had enough money, I'd use Ombrello on the whole glass roof as it lasts much longer and is much more effective. See: http://www.audi-a2.co.uk/omb.htm
[img=left]http://www.a2forum.net/stuart.gif[/img=left]Stuart Diamond: A2OC Founder | Forum Administrator