The moisture is finding its way in from a crack or seal in the headlamp lens assembly. The only way to repair that is to replace the lens assembly. I recommend checking on ebay or an aftermarket parts supplier on the Internet. You should be able to find the assembly for 30 to 40 dollars. If you get one at the dealer, it will be much higher.
Let me know if this helps, or if you have any other questions.
Wednesday, October 22nd, 2008 AT 9:26 AM