I purchased a 97' 540i/6 about 3 months ago from someone who referred me to this board. I have been lurking the boards ever since and have got some valuable info from you all. It seems I finally found my place to jump in and contribute. I have been an auto glass installer since 1993. The first thing I want to say is that the "COVER" is a molding around the glass. It is there strictly for cosmetics.
If you are experiencing a water leak, you have another problem other than this cosmetic "cover" (molding). If you have an air leak, than you hav another problem other than the "cover" (molding). If you have a an air noise, it could be from your molding catching air in the wind stream. BTW "cover" must be a BMW word for it, but from here on out I will call it a molding (it will be easier for a glass shop to understand what you are talking about if you decide to have it fixed).
My guess is that the front is getting dried out more than the rear by the blistering air from driving.
If you even think your windshield has been replaced before, I don't recommend spooning in the new molding. I can almost guarantee that you won't have sucess(unless someone used very little ureathane/glue)
For the member who said he used silicone, I hope that it was not silicone that you used. Silcone traps moisture and causes rust to form. More so if your windshield has been replaced and the technician left behind any bare scratches(even if you can't see them.
Be carefull who you use to replace your windshield because it is considered more of an art form than mechanical. I could go on and on with this, but if you need something, just ask. I plan on changing mine soon as I get some time. Not broken, just pitted. If I find some editing software I will record it and post it. With some of the projects I see you all get into it will definatly be a breeze.
I take forever to type so i'll wrap this up.
O yeah, unless the technician took his time, most experienced techs can look at a BMW and tell you if the windshield has been replaced before even if it has BMW glass in it.