I had the same problem with one of mine as well and went to dealer and he cut me a piece off a lon roll the right length. Slid the slide out about 6 inches sprayed the slit on the seal with silicone spray, and using only my hands was able to snap the new seal properly onto the slide frame lip. Took me a few trys to figure it out but once I got it going it was a snap. Cost me about $40 for the new seal. Make sure you take a piece of your old seal to your dealer so you can get the right type. If the rig is under warranty get them to do it by all means. It's about an hours work. Hope this helps.
Don & Pat Allen - Texas Boomers - Honorary Oklahoma Boomers
2003 Keystone Everest 323P - 2003 Dodge Ram 3500