It was an easy fix. I ordered 2 end caps, which are packaged separately, and a package of rollers-called roller-stud assembly. The rollers come in a 4 pack.
It only took me about 5 minutes to replace those parts on the upper rack.
All I had to do was remove the end caps and slide out the upper rack. I used a screwdriver to help remove the old roller assemblies. The new ones snapped right on. I rolled the upper rack back into the slide rails, and snapped the new end caps onto the the ends of both rails. It's as good as new. They also provide videos to help you with your repairs.