Resealing the Taillight Assembly

I am seeking any information on a procedure to follow to reseal the taillight assembly for my 98 Buick Regal. Water has been leaking into the assembly for some time. It is now causing major problems. It has caused a "rotting" effect in the running and reverse lights in the assembly and has killed two of the bulbs. I am interested in resealing the assembly but don't know where to begin.

Thanks in advance for any advice! :cool: