It sounds like the black plastic edge piece that is right angle rigid plastic at the end walls. It frequently cracks and then pieces fall off. I replaced them on my previous '04 Cruiser. Not that hard to do if you can get the replacement parts. There is no need to remove the slide out. Just remove the aluminum side trim at the bottom of the slide out end walls. Then with the slide open, use a bottle jack and wood blocks to jack up the slide out, just enough to take pressure off floor. Remove the old plastic (breaking it into pieces). The new piece will slip into place from inside the RV. It has double sided tape on it, so remove just a small part of the brown paper first, then from underneath remove the rest. Then re-install the aluminum trim including caulking. A couple hrs work.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK