GM Repair Problems? Ask GM Repair Expert Now.
Has the windshield ever been replaced? I just had the same problem on another H2 where it was leaking at the top of the windshield. It would leak into the headliner, down the a pillar and onto the floor. We identified the source by pulling the headliner down slightly in the front and running water over the vehicle.
So sorry for the delay! Yes it could be a body seam. The key is to have someone else help you. Remove or pull back the headliner and have someone wet down the car. Then you are going to look for the highest point where you see water coming in at. Does this vehicle have a sunroof? That would be a very common place to look. The drain for the sunroof could become blocked and water could spill on to the headliner. There are two small tubes that drain the water on the front corners of the sunroof. Look to see if they are broken inside the vehicle or if they are blocked.
Have someone drench it with water while you pull the headliner down a bit. It's got to be a body seem or something. Does this vehicle have an xm radio antenna on the roof? That is also a common cause of water leaks.
See if water is coming in at the antenna