I am not an expert by a long shot,---but when you say it is "mashing the gasket on one side real bad", it scares me for you. Sounds like the slide is not tracking even on both rails, which can and probably will cause more problems down the road. It will ruin the seal for sure.
If you are not sure what to do, get it checked out by a honest repair facility. Ask around and go with the place that feel right. Ask them to do a thourogh inspection of your slide. Money now will save money in the future while you are camping.
Steven & Darlene Rees (Jacob & Nicholas)
2011 Chevy Siverado 2500w/Duramax Diesel
2013 Elevation 3612