You gotta let it air out to dry. The Garage should be ok.
Oh also don't feel so bad lol, after all the heavy rain we had recently, I noticed that on one of my tail lights....it finally happened lol. I had a tiny bit of condensation in the same gap area as you....but it's going away nicely.
Ok. I took a look at the pix. yeah it looks like since there is a slight gap on the edge, the condensation happens. I have that same gap as well, but I haven't had that happen. It's probably just a fitment issue being that these things are aftermarket. Not sure if there can be a way to alter it to get a tighter fit. I would ask some of the other guys in the E39 forum about that.
They do look nice. I wouldn't say you're being "picky" about it, but i can see how it would annoy someone to see that every time it rains or you wash the car. You can try to seal up that gap as best you can without making it obvious, but there may still be some condensation still.
I didn't notice a gap on mine at all. Might be a new manufacturer of the lights that is making them that way. I agree with you on the condensation thing. it drives me nuts to see that. I haven't seen it happen to mine though.