I have not heard of this being a common issue all I can recommend is take off the panels and look. I dont have vent windows either but have taken the panels off and noticed that ford has an inner skin that had quite a few bolts going through looked like it could be compression or sandwiched together to hold in the window. Mind you it has been awhile since I took out the panels and that was not what I was looking for so I am not sure but it did make me wonder.