This has been an issue since 2009, nothing new. I have a friend that use to be a SA at my dealer when I called him about my 2013 leaking, he told me this is THE most common problem they have, fixed on a TSB IIRC...that was in 2014. One of the first things I did when I got my truck was to RTV the shark fin, add LED to the 3rd brake and cargo, when I took the assembly off, it took very little effort to turn the screws, when I put it back on, I tightened them fully and evenly doing the center to outside in a few increments, but not overly tight (can crack the housing). I haven't had any leaks (knock on wood), even when my rear window surround was cracked, never leaked.
I have a new one on order that I had paint tinted and will see what gasket it comes with and if it's the porous sponge that is on them now, I'll remove that and put my own weather stripping on it and smear clear RTV on the outer surface and install the new light in the same fashion I did above.
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