I followed the tips on ThriftyFun for corroded contacts, exhausted batteries, etc. After verifying with a voltage meter that the switch worked and the contacts all through the circuits to the motor were not corroded (battery compartment like new), I was able to verify that when batteries were in the compartment and I pressed the switch, there was a 6v current at the engine contacts.
The motor was frozen. I sprayed it both inside and out with WD-40 and let it sit for a minute. Still didn't start. I pressed the switch button and held it down and started tapping the motor casing with a tack hammer very gently. On the third tap, it started up and has been running ever since without a problem.
To get to the motor, take out the fluid bottle, remove the two chromed Phillips head screws holding the front fascia plate on, then remove the single screw down the swivel at the bottom. Lift up the plate to clear the swivel hinge and pull down slightly and the fascia comes out. The motor and pump are now accessible. To reassemble, put the fascia back on and replace the screws. WD-40 in the motor should prevent future water based corrosion from seizing up the motor shaft.
