Product review (1 stars): Don't buy this garbage!
Do not waste your time buying these replacement parts, as stated above, they are the same inferior quality that will fall apart again.  I had this same problem and did my own fix for these parts.  You really don't need these "wheels" to turn, you just need the wheels to stay in the tracks so you can pull and push the rack in.  These wheels will continue to break if you routinely fill up the top rack with dishes.  Which is silly, since I'm sure most of us bought this large capacity washer because we have a lot of dished to wash!
My fix was to actually glue, YES GLUE, these wheels back on with a hot glue gun.  They are now stationary (they don't "roll"), but the rack slides in and out with no problem and I don't have issues with the rack "sagging" when it is fully loaded.  I did this over a year ago and haven't had a problem since.  I first tried using a thin wire to attach the wheels back, but eventually that rusted and that's when I came up with the glue idea.  I can't believe the cost of these ridiculous wheel replacements and you can't just buy the wheels themselves.  I've had the same problem with the lower rack--all the wheels came off! Unfortunately, I didn't know when they came off and a couple of them ended up melted at the bottom of the dishwasher on the drying element. Also, can't buy just the wheels, which is ridiculous--instead they want you to buy a $30 assembly, which you would need 4 to replace them all, and of course, you already know it will break again!