I just started to get this in one of my headlight units, only on one side :S I found out why in my case, When I took the main beam cover off to replace the bulb the piece of sponge material that lines the outter rim of the round cover had fallen out into the engine compartment! I replaced it and its all back to normal, I think they're designed to absorb the moisture, If that doesn't work, Vovlo have developed a new cover with a breathable membrane allowing moisture out but not in apparently, I can't see them being too expensive so might be worth a try :) Hope this helps, Josh