My headlights are constantly misting up on the inside to a greater or lesser degree.

I have tried blowing hot air through the headlights with the bulbs removed this clears the moisture but it returns over night. I removed the units sealed the edges with silicone sealant dried them out again and it returned once more. My local garage said run the car with main beams on for 1/2 an hour but that did not remove all of the moisture, only in the area of the main beam bulb. have you any suggestions I do not want to pay £400 for new units there must be an easier way the car is 6 years old and apart from this problem the lights are pristine.