The head lamps are sealed and the only entrance into it is the bulb compartment cover. I was told that the rubber seal on the covers will go bad ofter awhile and this break in the seal will cause the condensation to build up. The rubber looses it's elasticity and form due to the high temp it's exposed to such as the HID builds and engine heat. Like with any rubber product, extreme hot and cold will cause it to break down. Try changing the rubber seal and see if that solve your problem. I've seen a post where small insects some how got into the housing as well so you know the rubber seal is no longer doing it's job.
2008 650 Convertible- 6 Speed manual- Sport package- HUD- Lane Departure- Comfort Access- Merino Leather- HD Radio- SAT