Beyond the excellent repair videos, a couple of tips:
1) with the agitator stripped, there is no way to hold the transmission from turning while trying to break loose the agitator screw - defeat the lid switch, set the machine to agitate and work the socket wrench against the motor.
2) the videos call for the use of penetrating oil when trying to free the spanner nut. This won't dissolve the many years worth of laundry detergent. Use vinegar to dissolve the soap first, then use the penetrating oil to prevent galling of the threads.
3) In my case, the spanner nut locked up again after one revolution. I used a hack saw to cut into the nut and a screw driver as a wedge to split the aluminum nut.
As good as new. I had gotten used to the noises it made to know when the cycles ended. I have to watch the time now because the machine runs quiet.