On my 9A slider I have a seal that works well, especially in flight. There must be some positive pressure there, as air always came in. I believe the slider must raise up a fraction of an inch, perhaps from lower pressure slightly forward. In the winter I could feel the cold air on my neck. I took a strip of vinyl upholstery, about an inch wide, and glued the front half of it to the slider. The back half of it is free and air attempting to come in presses the back half of it to the rear deck. It is very effective. It would be easy to try, even taping it in place might work.
Bob