Google search. Found AppliancePartsPros.com. According to their site, the piston was the problem 49% of the time, even though other knowledgeable people were saying that it was most likely the pump.
Since the piston was only $17, and an easy fix, I decided to try it. Two days later I had the part, and ten minutes later, I had it installed.
Ran the dishwasher, and it worked properly!
We were prepared to go spend close to $1000 for a new dishwasher.
Very pleased with AppliancePartsPros.com!