Have you raised the bed and tightened down the large metal plate with the motor attached to it. Mine only had two screws, the carpet and padding had compressed and was rocking slightly when closing. I drilled 4 additional holes plus the original four mounting holes and now it seals better. Make sure the three rollers are intact (above the seal in question) and the material above them has not been wet or starting to degrade allowing the slideout to sag.
1999 F250 w/7.3L Diesel
2014 Silhouette 299RKDS
Nights Camped 2016 - 21
He who dies with the most tools, wins!