I bumped into my KitchenAid dishwasher and the upper rack adjuster cracked. There was already a crack on the notch of the housing where the handle (lever) sits. In addition, the positioner popped out and I couldn't find it. So, I bought the three parts from AppliancePartsPros online.
It arrived in about a week. The repair was fairly simple, but it still took about 45 minutes because I didn't want to crack the assemblies.
For the housing, use a small slotted screwdriver to carefully remove the cover from the housing (you do not have to remove the lever). The Positioner was a little tough to remove from the rack. It as a little tight and you have to tilt it a little to angle it out.
The rack adjuster was also tough to put in. Taking the old one out seemed easy. There are actually two positioners. The other one is elongated. That one was also tough to take out and put in because you also have to angle it in. And, you must remove the small positioner before you remove the elongated positioner (reverse order when installing).
The rack adjuster itself was the toughest to put in. There are two notches near the bottom which fits into the rail. Angle in the inner notch first. Then snap in the outer one. It is a tight ft. Go slowly so you don't break the plastic. Once the bottom notches are in place, you put in the positioners.
You might be tempted to remove both adjuster and totally remove the rack first. But it would take twice the effort to put the adjusters back. I just worked on the broken side, being careful not to drop the rack. Also, it helps to the have the other (good side) visible as a sample when installing the broken side.
When ordering, make sure the housing lever is pointing the correct direction. After installation, the rack is now rolling steady and can be adjusted up or down.
When adjusted down, make sure the tallest dish at the bottom does not hit the rack sprayer. It can actually touch the sprayer a slight little and the dishwasher would still work correctly.
Good luck on your repair. The KitchenAid dishwasher I have is extremely quiet and works beautifully.