Just a question out of the blue, do your rear lights fog up? Will with the Pontiac Grand-Am brought some replacement lights for his Pontiac and they fogged up inside in a few days, like moisture is getting. I know your lights are a little different, but similarities there.
Re the tail lights: Yes, they are notorious for it! The tail lights with smoked-effect lenses de-laminate due to changes in temperature and moisture gets in. Mine were getting so bad they were filling up with water. I sourced replacements but the same thing happened again within weeks, so I'm not replacing them again. I have drilled small holes in the bottom of them so at least the water can drain out. All the models with similar rear lights seem to be prone to de-lamination to some extent - Grand Am, Grand Prix and Bonneville. I have seen it on Firebirds too.