I'll be darned! You're not going to believe this, I had the same thing happen to me last weekend. On the same side also. The gasket started flopping against the windshield and got my attention enough to make me pull over. I discovered it was stuck down with butyl and that the butyl had dried out. There is a cap that you can pry off that exposes a little plastic nut, but that won't solve your problem. Don't worry it won't come completely off because there's a screw holding it down. I haven't gotten into mine yet but it looks like the whole thing has to come off and new sticky-stuff (butyl) needs to be applied down. Below is a link to what it's called and the parts around it. (no affiliation)
Particle Filter Cowl Panel Covering