I'm another who just recently gave it a try.
I don't think I came anywhere near "waterproofing" my Arc LS Hybrid, but I did manage to get it open, drain the rainwater out of it, clear all the silver epoxy out of the threads that hold the head together, and remove the small amount of corrosion inside.
When I was ready to reassemble (after a through cleaning and drying) I treated all the electrical contact surfaces with DeoxIt, and very carefully put a thin bead of clear silicone automotive sealant between the optics and the front of the head and in the threads that hold the head together.
I purposely left the joint between the circuitboard and the rear of the head unsealed and trusted the o-ring between the head and power pack for the weather sealing at that end. I did that because I did not wish to interfere with the heat transfer to the head.
So far this seems to have worked quite well.
I wouldn't want to immerse my Arc LS hybrid in water and leave it, but I trust it with casual contact, spalashes and rain (which I could not before - it about 1/4 filled the head with rainwater when simply used in the rain).
It has ventured into the same conditions since I worked on it, and there is NO evidence of any water geting in.
The only "problem" with my fix is the damage to the finish getting it open the first time because of the threads being epoxied (no, it wasn't Loctite).
Good luck if you give it a try!
-= MICROSOFT FREE ZONE =-