I have replaced the slide out seal on my Jayco just two years ago. My only complaint was Jayco sells the seal in one length only. Regardless of size of slide out. Had to grab my wallet!
Anyhow, easy to replace from the exterior of mine. I retracted the slide out about 6 inches, pulled off the old seal (with care and this is where you will see where the rusted "staples" come from), cleaned all mating surfaces, installed the new seal, and trimmed the ends to fit. I cut the two upper corners of the seal that come in contact with the slide out for a tighter fit and made sure that the horizontal part of the seal overlapped the vertical sections to prevent water from being directed inside the seal. I then used a high quality white silicone sealer along the horizontal section and down approx. 3 inches down the upper corners where the seal meets the RV body on the vertical sides.
So far, so good. No problems or leaks. Hope this helps.