Well, I'm a bit disappointed that nobody was up to adding any words of wisdom before I took on this task, but I decided to just jump in last night.
Getting the cover off is way harder than it should be, as the 10mm top nuts are on so tight to the little bushings that keep the plastic from being crushed that the studs instead unscrew from the block below. No biggie, except that the front one also holds one side of the magneto in place. I was able to remove two of the three studs from the cover (one just wouldn't budge, and the plastic was deforming... time to quit and just use it as is). The air gap to the flywheel seemed to be around 0.010-0.012, so I reseated that stud with a feeler gauge in place rather than just blindly by way of the top cover nut.
There's plenty of slack on the fuel line so no need to drain the tank. Just lift the recoil starter / cover / gas tank assembly straight up and swing it off to the side. As long as you are below a quarter tank or so, there was zero loss and no fuel odor.
Two 10mm bolts, a zip tie, two #2 Phillips ground screws and the +12v spade terminal connect on the bottom hold the starter assembly in place. A little jockeying (I thought for a second that I'd have to remove either the muffler or the oil dipstick tube to get it out, but only the dipstick itself needed to be pulled to make that extra few mm of room to get it out.
I bench tested it, and sure enough it ran slow, sounded like marbles in a can, and the pinion would not rise.
Cleaned it externally, and began disassembly.
It's a gear reduction starter. That multiplies torque (making it possible to run with such a small battery), but the reduce RPM means it has to be well lubed to enable the pinion to track the worm gear against the upper spring.
With the "Bendix / gear" assembly off the motor (4mm hex Allen?), the motor on it's own ran quiet and strong. Great. Set that aside - don't mess with what's running well! Once a long time ago I had to do brushes on an abused lawn tractor, and that wasn't fun....
Sure enough, the upper section was pretty trashed. Grit and lack of lube had scored bearing surfaces, but it polished up better than expected. A touch of light grease on bearings and gears, a very light oil (Kroil and a dab of TriFlow - applied then wiped off most) on the pinion slide shaft and worm gear, and it moved like new. Reassembly and further bench testing showed that from a dead stop the pinion would now move about 2/3 of the way up towards the upper rubber bumper. Not as high as I would have liked, but enough to engage the flywheel ring gear.
Reassembled and tested. Several painless starts last night, and again early this morning. It looks to be good to go for another few years! Fingers crossed....
I did take pictures, but it doesn't sound like there's enough interest in this thread to warrant making an annotated service procedure out of it.