E92s don't have any seal for the lower part of the rear window.
http://www.realoem.com/bmw/enUS/show...diagId=51_6087
The E90s do have them though - Retrofit
?
http://www.realoem.com/bmw/enUS/show...diagId=51_5644
You are probably better off going to good paint shop to see if they can touch it up in a way, so it doesn't run to the exterior, and probably so it doesn't give you any rust issues (not sure if the trunk is steel and not alu.)