As an experiment, and understanding that you have a tail light seal issue, why don't you try removing the antenna and sealing (temporarily) the hole.

Then hose down the top of the car (not the tail light) and see if you are still getting the water leakage.

You are going to have to take the antenna out anyway to replace the seal.

I'm not sure how much humidity you get, but I live in the tropics/sub tropics and let me tell you - we have humidity. I don't have condensation in my boot. I don't have leaks either - so I'll give you that.

Did you manage to clear the front window drains? Have you poured water down them to see if its coming out under the car or flooding into the footwell.

Sometimes tracking leaks is best done with 2 people and a hose and just track back where it is coming in. A bit of a pain and time consuming but sometimes the only way.

I feel for your frustration.

Cheers

__________________
1988 W126 420 SE

beware of fundamentalists!