Replace roof seal on slides

[Justus2]

Here it is, another year and another problem with my 2014 Alpine(3010 RE). This one is our fault, we haven't conditioned the rubber seals at all, and push the slides in for winter, out in the spring.

The slide in the entry side of the trailer is leaking from the top. I need advice on replacing that rubber seal.

How do you do it?
Where do I go to get the right seal?

Is it normal for the rubber seals to shrink so.much that it leaks right in the center of the slide?

Thank you in advance ....