Looks like good ol' Bavarian Motor Werks screwed the pooch with the design of the headlight housing, specifically the seal. I have had this problem 3 times already on a 2006 E53, with the eventual results being a blown Xenon bulb, and this last time it was a blown turn signal. And obviously I'm not the only one with condensation issues.

It's definitely a warranty issue and the dealer did address it, but very annoying nonetheless.

Might not just be an E53 issue, as a buddy of mine just had the same problem on his 2004 330xi.