Hi everyone, I made the Tesla Gurus video linked to earlier and just thought I'd clear a couple of things up.
During the making of the video I had those light units in and out of two Model 3s multiple times. I can tell you that the plastic trim you have to pull back to get to it is pretty strong and flexible so you won't damage it. You could damage one or more of those plastic fasteners though, but they can be bought very cheaply from ebay. I really would advise buying a popper removel tool as well (preferaably plastic or coated metal) as it makes getting them out of the boot lid much easier.
WRT that foam piece which goes around the electrical connector, that was an annoying mistake on my part. I put the light unit back into the boot lid and then saw the foam piece on the floor so assumed it had dropped off. Someone on YT pointed out the error and when I went back to that light unit and took it out again, I had actually installed it correctly in the first place, so there was one gasket on the outside and one on the inside. I'd picked up a gasket which had fallen off another one I'd been repairing. D'oh! That gasket is only there to prevent water entering the boot around where the connector comes in but I wouldn't expect much water to get in there whatever happens.
These light unts were never meant to be hermetically sealed. There are little gaskets around the 3 bolts at the read, and the silicone gasket in the connector, and of course the Gore patch, but if a little air manages to get into the unit it wouldn't cause the sort of fogging a lot of owners see. As a couple of people have said, the real issue is lots of water from rain or washing getting in by capilliary action through the gaps in the plastic weld. If that weld was done properly, the Gore patch would eventually vent excess moisture out and there would be hardly any moisture inside to condense in cold weather.
Maybe the whole plastic welding process has never been properly perfected, as there are lots of other manufacturers suffering from this. Regardless, my feeling about this is that we can either keep throwing these lights in a bin or take it into our own hands and fix it ourselves. I know some have said "why DIY when Tesla should exchange", but look at the eMMC debacle where many owners have had their MCUs fixed by a third party because they're fed up with waiting for Tesla to do what they should have done ages ago. I had one unit replaced by a ranger but cancelled the second appointment I had booked so someone more deserving could get my appointment slot. I've got no problem spending a bit of time fixing this sort of stuff, especially as I know it will then be sorted for good.
Thanks for the positive comments on the video and if you have any other questions about it I'll try to answer them.
Cheers
John