Not meaning to thread jack here, I'm just in the same boat but on the other side of the car.
I tried sealing my bolt points on the tail light as well as the plastic triangle at the back of the rear window (by the tail light) and that helped alot with the leak, but i'm still getting leaks.
Note for everyone: use new silicone, i used a tube i had lying around and it never dried... ever. Had to do it again.
Someone suggested to me that i find an experienced body shop and ask them where cars can have common leaks like with body panel gaps and such