Thanks to this site, I was able to get the repair parts from Geno's. In my case, the plastic teeth broke off the sprocket on the end of the big screw. The worm gear on the motor was still intact.
I bought the kits from Geno's. I needed one for the front motor and one for the rear motor. One requires a longer drive screw than the other (by 1/2"). I don't know that these are OEM, but I suppose they could be. They're definitely high quality pieces. The wheel gear on the drive screw is steel on the new piece. The included worm gear is plastic just like the original. So, the weak link (plastic wheel) was addressed by swapping steel for plastic.
I watched the various videos on YouTube. None were very good, but I got the gist of the operation from them. The actual seat is secured to my tracks with four 1/2" (not metric) nuts. Release the switch per the videos and disconnect one seat belt connector and the seat comes right off. It makes no sense to me to attempt to remove the whole assembly and work on it that way. Pull the seat, then pull the track assembly. Then, take it to your workbench and do the surgery there.
I used a large C-clamp and a socket to get the knurled pins started. Then I was able to carefully drive them out using a cold chisel under the head. The roll pins are the big challenge of the job. Geno's tells you to drive them in, cut them off, then drive the rest out. The pins will be shortened, but still usable.
I used a new, quality set of Vice Grips with nice hard, sharp teeth to grab the inboard end of the pin and use various pry tools and spacers to "pull" the pin out. No hammering required.
Once these roll pins are out, you're over the hump. Now, you just swap out the kit parts per the instructions (very straightforward) and prepare for reinstallation.
You can drive the roll pins back in without too much trouble, but you could also use ordinary 1/4" pins (with holes for cotter pins) or 1/4" bolts or something similar. I don't think the roll pins are absolutely necessary. The knurled pins at the end have to be driven back in, but they don't put up the fight that the roll pins do. You should use a heavy mass backer to hammer against, otherwise it's much more difficult to get them in.
Upon removing my motors, I checked the mechanism for freedom of movement. It was extremely stiff - almost frozen. So, I applied oil to all pivot points and gradually moved the mechanism through it's travel and "watched" it loosen up dramatically. Back and forth, back and forth, until the oil had worked its way into the joints and freed things up. Once it was all nice and smooth, I put the motors back in.
I set the mechanism back into the truck and tested it. Works like a charm! Nice, smooth, quiet action throughout its travel range.
I would not call this job easy, by any means. But, if you're good with tools and have some inginuity, it's fairly straightforward. But, I can't condone the brute force approaches I saw on YouTube. They're just not necessary. All in all, it took me most of a full day.
Yes, you could purchase the complete motor assemblies and save some work. But the work you save is easy work and for all we know, the new assemblies have the same plastic wheel gear as the originals. So, I'd say getting the kits gets you a better and cheaper result.