I just wanted to add my experience to this thread. I'm sure there is plenty of information out there but I had a fogging issue on my driver's side headlamp, pretty bad actually. There was condensation building up to the point that after the required 4 hour time frame from GM (they said moisture should go away by 4 hours) it was still there. I went to my dealer and even thought I had put the HID kit in from theretrofitsource.com, they warrantied my headlight. (the cost of the headlight was 910 if I had to buy it!!) it's been 3 weeks and NO FOGGING issues whatsoever now. there is a slight film of moisture if it is highly muggy out and then gets cool, however, this goes away very quickly as the vented headlights should. Just a note on the HID install, I did place windshield glue on the outside of the hole that i drilled into the headlamp cap and I think this helped, but I can't be sure. Bottom line my dealer replaced the headlamp and now I have no issues. Hope this helps someone!!