Product review (3 stars): CALL KITCHENAID
I did, and after waiting on hold it did not take long for their representative to send me two of this part.  They must be aware of the issue, and although it's clear the design materials are crap, they agreed to send out the parts without fuss.

I called armed with my model number and serial number, and I called the part 'the wheels attached to the upper rack,' specifically because the 'nylon disk racks' are included in the 5 year part of the warranty (my washer was 2 years old when the wheels gave out).