[joehawthorn65]

I ended up taking my Terrain to my normal independent shop. He said there were two factory cut holes along the pillars of the rear hatch that had some type of tape (like a thicker duct tape) over them that had deteriorated. He said he put a new patch and seal over the holes. It seems to have stopped the water getting in for my case. Honestly I think you'll have to just take it somewhere and have them run their water test to find the leak. My mechanic had my truck for 2 days hunting down the leak. He had to take interior panels off to find out where the water was leaking from.

Right on. tape is the answer. Just remove right rear tail light assembly you will see the taped area.