Definitely cannot be the stopper, the stopper is waaay to the left and below the leak. Also with pouring rain, checked on the other side of the stopper, bone dry.
The tail light is way below the leak, and a lot to the side. Inalso sealed the tail light with silicone to completely take it out of equation.
The only thing I can think of right now is possibly damaged rear drain hose. Maybe water is escaping from there, and running down the D pillar or something. Cannot possible see what else it could be.
Two years ago I redid my headliner, and zip tied the drain hoses, so I can't see them coming off loose either.
I'll have to pour some water and try to do more testing. This is weird