Yet another problem with my 03

For a car that hasn't had a problem for 6 years, it sure has taken a turn for the worse in the past month. Now, I noticed that water is pooling up in my trunk around the spare tire. I think the stripping around the taillights might be the problem, but I'm not sure. Anyone have any solutions?

I figured it out. It's definitely the gasket around the right tail light. Should I just use silicon around it, or replace the gasket all together?