I went to the carwash the other day & the trunk had water in it afterward, I was thinking that maybe one of the workers left it open, But today with heavy rain there's alot of water in it.
In 2007 the right rear quarter panel was hit & replaced. The trunk wasn't damaged but was removed by the auto body shop to do the repair. The seal is intact but I just noticed there is free play when I push down on the trunk. This car has been washed 100's of times since it was repaired in 2007 with no leaks.
Is it possible the trunk latch has to be adjusted to make the trunk tighter? Resulting in a tighter seal? The big question is: Is the latch adjustable?

 

If your trunk seems to be sitting flush then that is probably not your problem. What i think your problem is that your drainage tubes from your sunroof arent attached properly or the black portion at the very end of it is clogged. There are two drainage tubes which reach from your sunroof to your rear quarter panels where they reach to the very back corner of your trunk. These then attack to a black rubber grommet that pass through the floor of the trunk, check these to see if your body shop had attached them properly and to see if they arent clogged.

 

Yup, that's exactly what the service rep at the dealer said too. I'm gonna have to check them.