Ok.... my lengthy and noble attempt to revive my dead opener has officially been called off.
The Reader's Digest condensed version:
1. Called the Genie support center, went through a step-by-step troubleshooting sequence, was told part "A" was the problem. Bought part "A," installed it, same broken opener.
2. Repeat step 1, this time, since part "A" had been ruled out, bought recommended part "B," installed it, same broken opener.
3. Repeat step 1 again, this time, since parts "A" and "B" had been ruled out and I still had a broken opener, they offered to send me the last thing it could possibly be (part "C") for free. Received it today, installed it, same broken opener.
From my third attempt at a troubleshooting session, I learned that if parts A, B, and C are not the problem (which they were not)... the only possibility left is that the motor itself is bad (worn bearings), and a replacement would run $150. When I cheerfully told the tech on the line that I could buy an entire brand new opener for less than that, she wholeheartedy agreed.
Plus/Minus of my attempt to fix the opener...
On the minus side... three weeks worth of troubleshooting sessions, ordering/waiting for/installing parts/testing/calling back.
On the plus side...I now know so much about this particular model of Genie garage door opener that I could easily get a job as one of their online troubleshooting techs! And the parts I bought (that were not needed) are returnable, so I'm only out the cost to mail them back.
And the happy ending... my son bought me a whole new opener!
And so ends the story of Harry and the broken garage door opener...