Are you still on the original headlights? I've never had an issue with mine. The original ones or the DII ones I upgraded to about 5-6 years ago. Maybe it's another weather related thing you know like rust.

 

Yeah I've had this problem with stock D1 lights and with the earlier D2 lights I have now. It very well could be road salt/weather related. I'm too cheap to source new lights, so I'll just blank off the holes for the City lights.