'07 S6 - tail light condensation remedy

My left tail light has moisture behind the lens. Odd as this is a no paintwork car, so it’s not like it was out for a collision or paint repair and the seal was compromised.

Have others with this chassis encountered such? If so, what was the source and what was your remedy? Left side marker too, but that I’m just waiting to swap out with smoked lenses so don’t care right now.

Suggestions / insight appreciated - thanks in advance gents!