I had water ingress problems when I first installed mine last year, but the problem was in the operator. I had failed to ensure the lead was firmly inserted into the light housing, and the light died after a heavy Danube downpour.
I thought the game was up for the light, but time, a little gentle drying by sun and hair dryer, and a reinstallation of all connections brought it back to life. It has worked flawlessly ever since, surviving several short sharp showers (although I've yet to encounter an all-day drenching such as that first one). I have considered packing silicone sealant around the plug if it happens again, since it never needs to be removed anyway. Permanently attaching the controller/USB lead is a good idea, although it takes away the option of not using it.
I carry a sandwich bag to throw over the light in case of a really heavy rain, but I've never had to use it, and I'd worry about the light overheating. Of course, the light can't be fully immersed, and rain that heavy would be no good for bike
and rider.
