I had the same problem with both of my headlights but the driver's side was worse. The problem was water collecting in the bottom of the lamp housing and splashing up on the hot bulbs. Nothing I did to seal the lamp socket seemed to help. I did lengthen the interval between burnouts by using a vacuum pump and hose to suck out the water each time. What finally did the most to help was drilling a couple of small holes in the bottom of the lamp housings. I drilled the holes towards the back of the housing to minimize water entry through them. I worried about the possibility of water entering from below but that has not been a problem and the water draining out of the housing through the holes has cured the problem. | 
