It's pretty involved and requires removing all of the plastic panels that touch it. The worst ones would be the rear corner panels. Before I did that I would just unbolt the roof rack, apply silicone sealer liberally to the bolt holes and put it back on. Let it dry and do the water hose test or go through the car wash. I mean, it has to be coming from the roof rack or the weatherstripping. The 3rd brake light, the rear window and the trim piece between the roof rack and the back window just don't seem possible as leaking and running over the door.