Tail light lenses hold water

I would replace it with a used one before the water/humidity causes electrical problems. It probably has a bad seal. You can find a used one online.

 

Both lenses?

 

A simple quick temporary fix would be to drill a quarter inch hole at the bottom to drain the water. Take out the bulbs and coat the contacts with dielectric grease to prevent corrosion in the contacts.

After the unit dries, try to find the water entry point and seal it. If found, seal the drain hole. too,

Works and a lot cheaper than replacement.