As I checked everything out, I found that except for the accumulation of 24 years-worth of dust and grime, everything (but the drive gear) seemed to be in good shape. The motor seemed fine but there was no way to test it. So I began to disassemble everything.

Two things became immediately apparent:

1. The specifics of my opener differed somewhat from the howto video and the instructions that came with the repair parts. Not a huge surprise here, I would have been surprised if they were the same! Nothing seemed insurmountable about it though. And...
2. The brass bearing at the end of the motor shaft seemed to have come loose from the frame mount and literally fused to the shaft. Hmmmmmmm. That was weird and disturbing. How to get it off? I need to get it off to get the worm gear off the shaft, and the worm gear's not coming off if the bearing won't. Here's what the new bearing looked like:

Seemed to be made of brass or some soft metal.

I can't show you the old one because I broke and sawed it off in 5 or 6 pieces. I used a screwdriver to snap pieces off the flange until I could extract the motor from the mount, then I used a saw blade to carefully slice down the side of the bearing (pictured below). I was not thrilled to do this because of the possibility of shaft damage but I felt I had no choice. I was very dubious about any of this working and was wondering about maybe just buying a new motor...they are $39.99 on eBay. But I kept going with the original stuff.

I had to use the same stategem to get the old worm gear itself off:

You can see some shaft damage from the saw blade but I thought that it would be under the gear and thus of little consequence. or at least that's what I told myself. The crinckley stuff beneath the gear are a couple of layers of aluminum foil and plastic wrap put there to keep metal filings from going into the electric motor itself. Finally:

I had to saw the old main drive gear in half to get it off the gear assembly that I previously unbolted from the motor mount, a super-bitchy time-consuming job. Here it is next to the new one:

This gear slipped onto a shaft (below) that held the chain sprocket and was bolted onto the main assembly by a steel plate:

You can see the spline that the main gear engages into (above).

The new worm gear also had to go onto the motor shaft and engage a spline. Since it had to be persuaded with a hammer to do so i was super afraid that I'd be driving it on and the slot would not be aligned with the spline. But eventually I got it in place.