Humm,,,I don't have a slide. But, when the slide is out there is a lip (made from a board) that keeps the slide from sliding out too far. When the slide is in you, or some young person, should be able to wiggle your self into a position to see the back side of this lip. It will be inside of the camper now. Is it possible that some moisture has gotten on the back side lf this lip between where it touches the wall of the camper when the slide is out? If it has maybe something is growing on there (mold, etc.) I'm probably wrong but, I thought I would throw this idea out there in case nothing else works.