DJW,
The lengthy and a lot of work way is to take the fairing off. The other way on my 03, which should not be much different that the 04, is to wrap the blade of a small slotted screwdriver with some cloth, then slide into the slots in the front of the fairing, gently force the tabs from thier slots. Do the bottom ones first when they are out gently pull down and away, the lens should come out.
You will always have water getiing onto the back of the lens when you wash or ride in the rain, eventually the heat of the lamps will dry the lens off. I would think the only way to keep water from getting behind the lens is to seal it off somehow, ie Silicone Seal etc., have never done this as the moisure behind the lens has never bothered me, plus may be to much heat build up in the headlight area, just a guess, I really do not know why HD made the fairung for the Road Glide the way they did, especially the mounting of the windshiel, should have had it like the EGs.
geezerglide