I can't help you as I'm no slide expert, but my guess is it's simply out of adjustment someplace. The mechanisms closing the slide are on the bottom. So if they have pulled the bottom tight, and the top is still out, there is simply no way the top is going to close. My slide as it comes in starts to tilt inward and the top contacts first maybe an inch or two before the bottom. Then the mechanism pulls the bottom in and this causes a tight seal at the top. You say you have adjusted the slide up and down, but is there some type of tilt adjustment on the slide?