NSN and Denisesb, I dont work for HL and just an owner like you. In NSN's situation, unless he checked to see when his coach was built (not year model). Its very possible that the slide seal was stuck to the top of the slide, and when the slide was closed, it tore the the seal off. It was exposed for awhile to heat and the elements. Maybe 2 years, we dont know. Still not his fault, dealer PDI sucked.
Denisesb, you might go on the NT site and see if there has been a problem with the slide seals.
Here's my 2cts, rubber seals are subject to the same things as car doors and window weatherstrips. They "do" require some maintence. Keep the tops of the slides clean. You should clean and lubricate them as regular maintenence. Some people swear by "303" that you can buy at CW. I have always used 3M dry silicone spray. It wont leave a film or get sticky. It's to each his own and what works for them. When putting out your slides make sure that all the seals are folded out. If not they could leak. Look behind the inside moldings and make sure you cant see any light showing through. That would be a leak. As RV's are moved around, things settle. Recheck all the seals every year, as you might have to make slight adjustments to the slides themselves. (its not hard). Just food for thought..... Bob