I've had mine for a short 6 weeks now. I've ridden with it in the rain probably 10 times (it's been a dry winter here). No issues with water getting into the lighthead. However, when I got it, I noticed the threads under the bezel were dry, so I put a slight amount of grease on them. I suppose that may have marginally helped with waterproofing.

I plasti-dipped the battery, so it's waterproof. Probably didn't matter thought because most of the time it rides in a Carradice Junior (a saddle bag that I use as a handlebar bag).