Product review (1 stars): They need to sell these as a six pack due to how often they fail.
This is pretty much the most poorly engineered part in existence.  At least it didn't kill people, so I guess I'd rank it higher than a Ford Pinto.  I'll place it on the same level as the fabulous rack adjusters where the wheels break off.  Yeah, we are a group of people that have been beaten and abused by corporate greed.

Here's a tip, if your dishwasher isn't cleaning and you can hear things going, it's probably this.  Before you attempt any diagnosis, check this part first.

In 2 1/2 years, I've had to replace 3 of these in a brand new KitchenAid.  They have a tendency to self-destruct when something else goes bad.  Of course it could be the pump motor, but you probably read up on that already about the faulty seals.

In fact, a few days ago my dishwasher wasn't filling up correctly.  After a lot of checking with a multimeter I concluded it was probably a weak inlet valve.  So replaced that and to my chagrin had the same symptom.  So on a whim, checked the chopper and the blade was off and the screen was clogged.  Apparently when it fills it needs to go through the screen.  Hope that helps someone.

Be sure to dig around and find the cheap washer that is probably laying in the water in the sump when you replace it along with the blade.