Would suggest doing a "Search" on the forum for Schwintek slides. There are multiple threads that discuss many of the problems the slides are having and some of the remedies. Water getting in behind the fascia seems to be a common problem and can cause problems like you are having. Some repair facilities recognize this problem better than others. Tell your dealer or repair place some of the things you find in these threads and have them start looking. A quick way to look for possible water problems is to look under the slide at the outside edge and see if some of the screws are starting to rust. Maybe even put a screwdriver on a couple of them, give them a moderate twist and see if they break off. Been there, done that, and had the coach gone for a long time. But, that was while all this was being diagnosed. If you find the problem maybe they'll be able to get it fixed quickly. Good luck.
"All fisherman are liars, except you and me, and I'm beginning to wonder about you.