I recently had to replace both tail lights on my '16 228i due to condensation that was so bad it caused the connector to corrode and short circuit the entire tail light board on both sides. One right after the other.
I replaced the lights with used assemblies from Ebay and everything works again, but despite ensuring that seals are tight and there was no condensation inside to start with, there's more condensation inside than was even in the original tail lights. I know this is an issue that BMW would remedy under warranty, but mine ended long ago so I'm at a loss.
Fog light condensation has also been an issue since I had to replace my front bumper (long story short, ended up with an M-Sport bumper kit and had it painted to match), but this is surely out of warranty as well.
I've heard you can buy new tail lights from BMW and they'll reimburse you whether or not you're still under warranty, but it's all subjective so I'd rather not spend $1000+ and cross my fingers that BMW will cut me a check.
That said, has anyone successfully dealt with condensation like this on their own outside of the dealer? Could really use some advice. My car looks horrible and it makes me sad.