[beeje]

Your slide should ride on a white plastic wear bar that runs the whole length of the slide. The black Darco covering should be one piece with no seams. It looks like yours was damaged by something caught under the slide floor when it was moving. My guess is someone put some kind of tape on to cover the damage and the friction of rubbing the wear bar pulled it off. With the slide 1/2 way out, look between the slide bottom and the camper floor for something that does not belong there. I would not worry too much about it since it should not get wet from the bottom.