leaking trunk, please help

My trunk has always been a little less than water tight, recently, im noticing that in a night of rain, i have a nice sized puddle of water in the left side of the trunk closest to the tail light. the weather stripping seems good, i dont know what to do.

"I used to say I live my life a quarter mile at a time and I think that's why we were brothers- because you did, too."