Sure it's the windshield and not possibly the heater core?? If not the heater core then I would suggest somewhere along the upper edge where the roof skin is spot welded to the window frame or cross rib. You may end up having to cut the windshield out, clean that whole upper seam/pocket out to bare metal, look for rust or pinholes, mig/repair the damage and put it all back together. Lost the windshield on the G-10 to a combination of stone hit and subsequent crosss-country wide crack and when I had the old window pulled, it was rust and holes that appeared. Had to do some serious rehab to rebuild the surface to be watertight again before a new windshield could be laid in. The techs used a two-part urethane adhesive-sealer than seems to be doing the job..