Water entering interior of Hummer H3 thru seat belts on 2006 Hummer H3

I have water coming through the seat belts on back seat side of my 2006 Hummer H3. I had noticed my mats were wet on several occasions. I just noticed water streaming down where the seat belts are attached/coming out of interior side of car near the back doors. The dealership wants $100.00 to check it out. I bought this vehicle used.

Asked by for the 2006 Hummer H3