Welcome to the Forum!
Yes, the insulation on slide out does wear out. Usually, it is just a rubber part (not cloth?) that slides in and makes the seal when compressed. I'm not familiar with your MH model, but I'm sure someone here will chime in with the particulars.
When you have time, be sure to update your "signature line" with your information about your MH and anything else that you would like to share so that we know more about you.
Fun and safe camping!
Colorado '15 Winnebago Forza 34T w/MKZ hybrid toad