You found the cause already. There can't be any moisture inside that can get onto the bulb. The housings are so well sealed that there even needs to be a rubber o-ring around the base of the bulb.
There have been service bulletins for other car models that describe where to drill a small drain hole in the bottom of the housing so leaked-in water or condensation can run out. Many newer housings even have small rubber drain tubes on the bottom.
Also be absolutely certain you never touch the glass part of the bulb with your fingers. Fingerprint grease will burn into the glass and cause a failure of the new bulb.
Tuesday, July 16th, 2013 AT 4:30 PM