The top and middle racks had broken rollers. Tracks were intact. Went to the website with the Model number. Pulled up drawings. Turns out the rollers are part of assemblies; for the middle rack "Rail-Pull out" left and right (mirror images of each other). Top: "Holder", which is a set of two.
Top rack: the Holders just snap on with built-in clips. Easy. about 2 minutes per side.
The Middle rack is a little more complicated. There's a spring-loaded clip that you push on, slide the rail assembly down, then you have to gently pry to distort the holder a little bit to get a stop clip to pass the wire rack. Took a while to figure out the technique, but after that about 2 minutes per side. They might want to do a video showing this.
Racks now roll in and out like new. I'm an engineer, and how they got broken was people pulling the racks out and slamming them into the stops. Won't put up with that for too long.
For the company, searched the part number on multiple websites. They had the best price for genuine products, not Chinese knockoffs. For ~$165, my $900 dishwasher is back to normal. Also have replaced, in the past, the drain pump and main circulation pump. A lot cheaper to repair than replace the whole dishwasher. Delivered from Georgia to Ohio in 3 days.