So 3 full months have sealing the tail light up with some silicate gel and it's holding up fine. There's also a rubber gasket in the middle of the tail lamp. If you take out the screws in the lamp housing, this gasket reveals a break in the plastic enclosure so you cans service the circuitry. It turns out for this light, the rubber was ever so slightly misaligned with the lip of the two halves of the outer housing. Here's a drawing:
Once I fixed this, it's been air tight.
On an unrelated side note: I decided to keep my car in drive with the e-brake on to see what these lights look like when I'm driving. They seem to be totally off. I wasn't sure if the afterburner LED strip was supposed to stay on — I think it's tied to the rear side marker circuit, so maybe not unless I messed with my side marker wiring.