Hey Bjoern! Well, I certainly wasn't expecting that one! This is the first instance of something like this that I've heard of so far.... lucky you! It would appear that either the combination of the cold temps and/or snow was somehow able to get by the water seals. Either that, or I just didn't do a good job of sealing it up in the first place. I've had several of these running in Canada and Alaska for a good while, so it's most likely my fault that it didn't get a good seal. Good news is that you should be able to disassemble the lens cover and re-seal everything with a heavier layer of grease, and you'll probably be alright. Here's what I recommend:
Remove the lens cover (see user's manual), and remove the lenses, and if there is any water directly on the lenses, blow it off as best you can (the less you can physically touch the inner surfaces of the lenses, the better). Set aside in a clean location to dry. RUN the light for 10 minutes or so on level 3 with the lens cover completely removed. You can do this inside with no air-flow. This should "bake" off any moisture that has gotten inside the housing.
There are three possible locations for water to get in: Around the perimeter of the lens cover, around the lens cover hold down screw, or around the lenses. From all the testing that I've done, It would be least likely for water to enter around the main seal (larger black o-ring) or around the screw. The most likely point of entry would be around the lenses, and specifically around the elliptical lens. If you look at the pictures closely, you'll see that the surface of the elliptical lens is actually ridged. It's very small, but you can see why this is a challenge to seal off. I've actually looked at this seal under a stereoscope and the silicon o-rings have proved themselves to be soft enough to conform to and fill these very small valleys.
Just to take it another level, when I assemble the lights, I apply and light layer of silicon grease to each of the small, clear lens o-rings before placing them into the grooves in the lens cover. In your case, it might be advantageous to also go around the edge of the elliptical lens itself, applying a very small "bead" of grease, just to make sure that all of the ridges stay sealed. You may also "paint" a slightly heavier layer of grease around the inside of the main lens cover "race" (see picture). Lastly, you should put a small layer of grease around the underside of the screw head that is used to hold down the lens cover. This screw needs to be moderately tight. Just tight enough to "bite" into the polycarbonate and form and nice "lock." This downward pressure on lens cover is simultaneously compressing the o-rings against the edges of the lenses, so if it's not all the way tight, you might not be getting the best seal.
Before you start putting things back together, just be certain that everything is absolutely clean. If you need to do any cleaning of the plastic parts, I'd recommend only using plastic-safe cleaner such as "Sprayway." No paper towels, only soft cotton. There are several other similar foaming glass cleaners available at auto parts stores (at least here in the states).
A few other tips and things to note...
Use a small pair of pointed tweezers for positioning the clear o-rings into place.
Use a small hobby paint brush for applying grease to the main race around the lens cover.
It's completely normal to see water droplets in the area highlighted by the yellow lines around the outer perimeter of the lens cover, in the small gap between the lens cover and the housing. It's only in the areas denoted by the red arrows and "X" that you want to see stay dry.
Never use any kind of detergent soap while cleaning, to avoid breaking down the grease on the o-ring seal.
You can find the silicon that you need commonly available at plumbing supply stores or on-line. Just do a search for silicon o-ring lubricant.
Lastly, once you have everything sealed correctly, you should be able to plunk the light into a sink of water for 30 minutes (see picture) with absolutely no visible sign of water entry into the aforementioned areas after you pull it out and blow it off.
The size of allen wrench that you need for the lens cover hold down screw is 1/16".
Let me know if you need any help with the process.
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