Product review (5 stars): Definitely Worth It!
Apparently, my Whirlpool dishwasher has a known issue with the seal going out on the shaft from the diverter motor (the rectangular white thing pointing at 10 o'clock in the photo) resulting in leaking.  The seal is not included with the motor, but in the sump.  This product supplies the sump, pump motor and diverter motor.  I didn't need the pump motor, but some people report running into problems mounting the pump onto the sump, so I decided to avoid that by buying the completed package.  Buying a sump and diverter motor is around $100, so it doesn't cost that much more, comes pre-assembled, and saves a little time and trouble.  All you have to do is swap the drain pump and sensor.

It was a very easy repair.  I had the unit replaced in about an hour, at probably less than half what an appliance repairman would have charged.