I had the same issue with my R34 head lights. Was a real pain in the ass because they used to fog up all the time. I had to do some repairs on my head lights. They are made of 2 parts, the lense and backing with some clips and a shit load of black sticky crap holding them together. I heated it with a hair dryer and pulled them apart (with a lot of force) then cleaned and fixed them. I then re-filled the grove with silastic and resealed it. I also filled the outsides to make sure it was 100%. It's a bit of a job but you can do it.
You'll find on the base of the lights there are some breathers too, make sure the rubber guards are on as water can get in there.