[EarlyBird]

correction "work drive" should be "worm drive". same thing as screw drive.

That sounds like one of the gears I replaced. It was long and looked like a screw. I also replaced a larger, round and flat, normal-looking gear. Both were made of plastic.

[SouthMountainBilly]

I've replaced the opener. It's a few hours work, if you can handle other simple household repairs (rebuild automatic transmission, replace tuner in TV, etc) then you can handle this.

Seriously, as long as the tracks/wheels are OK, the opener itself is a snap to replace. Although, it might help to have two people, they can be tricky to hold in place while you bold it in.