Paul -
If this were my situation, before I was to accept that the transmission locked-up (that is not common), I would trace the problem a little further by removing the belt and turning the individual pulleys. First, the motor (I HAVE had one or two of those suddenly and rather violently seize, one when my face was inches from the motor as I inspected the workings). Then, I would check the pump - they commonly lock and cause burned belts, etc. and might even over-torque the motor and make your breaker trip. Lastly I'd check the basket drive pulley, however it is probably fine. With the belt off, the transmission pulley should freely rotate in either direction, even while engaged in agitate.
The locked agitator is quite possibly due to the machine having engaged agitation before the clamity. Once they do that, they are properly locked and nothing is wrong. It is nearly impossible to turn a locked agitator except in a highly worn gearcase, at least in my experience.
As to available parts, there are a few transmissions out there, though the new ones I've seen have been around $150 before shipping. New agitator shafts are TOUGH to find, but you shouldn't need one if you have a drive-block (bakelite) agitator unless it has significant grooves worn in it.
My bet is on the pump or motor.
Btw - that new snubber may become noisy after while - they make this wicked rubbery sound when they wear-in and it drives me nuts. Rubbing them on a cement driveway to scuff them up a bit once this happens was Whirlpool's recommendation.
Gordon
[this post was last edited: 5/25/2010-10:11]