Product review (1 stars): Don't buy this!  Just call warranty dept and tell them to replace whole upper rack (under warranty for 5yrs)
I had the same issue as many folks here - plastic piece for roller wheel broke on several of these.  I was about to order W10712394 replacement assembly when I read a review that said if you just call Whirlpool warranty dept and tell them the nylon rack is defective (it is, due to the defective adjuster assembly W10350376) rather than saying you need a new adjuster assembly, they will send you an entire replacement upper rack.  I was surprised this worked, but no questions asked.  Refer to the warranty language on pg 18 of the dishwasher instructions.  What a racket on their part!  They should just buck up and offer to replace the defective adjuster assembly for free.  They will tell you that you void remaining warranty if you install it yourself (pitching their install services).  Again, a racket.  I hope this amounts to enough aggregate consumer scamming at some point to get interest from a plaintiffs lawyer to file a class action lawsuit.