Check this out, I had water in my spare tire well also. There was a seam leak up at the right tail light area. The seam seal material that they use to seal all sheet metal seams interior of trunk (you have to remove all interior panels & floor pad from trunk to visually inspect.) was not done properly in this area. The dealer told me they brought in a "water doctor" to check my trunk for leaks. He supposedly went into trunk, had someone hose down from outside. He reported no leaks. Yeah right! The next day after I picked the car up after leak was supposedly fixed, it rained. Guess what? Yeah, there was water in the tunk. I took it upon myself to find the source of water in the trunk. I used a half cup of water, with trunk open, carefully poured the water down the drain trough right side of trunk opening (outside of deck lid weather seal) and viola......! there was water running into the trunk through a badly sealed seam instead of down through rear bumper area. There are two small holes at the ends of those two toughs that run along either side of trunk (near top inboard side of tail lights) to let water drain to the outside. There is also a service bulletin out by GM for 2000-02 Bonnevilles. The number is #01-08-57-005, it has the title "Trunk Area Leaks", and addresses four different locations where water enters trunk on these Bonnies. The prob that I have with my water leak is not addressed by this document. Anyway, hope this helps a little.
2003 SSEi, Light Bronzemist Metallic - All Stock For Now
IBEW Local 261 Groton, CT
My other vehicle is a nuclear submarine.