VERY common problem...below is the best write up I've found that involves no cutting of the headlight assembly and no "baking" of the light to soften up the headlight seal. In fact, some headlights, like mine, won't soften up no matter how much heat is applied because a different type of sealant was used.
Anyway, I can vouch that this procedure works; I've done it (with a few tweaks of my own, like snapping the new adjusters together before reinstalling). If you are handy, you will figure it out.
http://forums.bimmerforums.com/forum...nt-(no-cutting)