FWIW, I just purchased a Beaver Contessa. The right headlight was fogged up due to leakage INSIDE the light. I found the cause to be the careless way they ran several screws into the housing in order to mount it.
I took it off the coach. Made two small 'bags' of rice tied into some of old pantyhose. Tied a string to those and pushed them inside of the light. I left it inside of the house for about 2-3 days until it appeared that all of the moisture was gone. Carefully extracted the rice packets and sealed the entire perimeter of the light (mostly where the screw holes were).
No more moisture and it didn't really cost anything.