The great Zardoz has spoken.

OK, I'm going a little grandiose here. But the image of the hovering giant head was too strong to go unmentioned.
Al has always got a most welcome big head for these kinds of things.
However, I haven't fed the big head enough specifically correct data to do the most good yet.
So I have included the , excuse the expression, "exploded view" taken more than a year ago as I was first taking the broken clutch apart.
Looks to me like it is the first gear clutch that shattered.
Other than the crankshaft whose damaged splines occupy only the last 1/4", that are not loaded upon automatic up shifts- I don't know what other damaged shaft you might be referring to.
Sorry if my previous information was too incomplete or misleading.
The smaller diameter basket shaped piece at the end closest to the camera, that is encircled by a spring, is the part whose internal splines were found to be stripped, with consequent damage to lesser degree inflicted upon the last 1/4" of the crankshafts splines.
The big plate at this end has a beveled face at its periphery lined with asbestos like clutch material, and is the alternative mechanism for engaging second gear.
This just in- a scooter specialist just called me to say that a dragging wheel at the rear, via low tire pressure, dragging brake, or bad wheel bearing could also be a source of generating an offset load that could try to torque steer the car.
That would particularly make sense if the loading were cyclical, like a bad bearing jamming up a bit, once per revolution. Could even make sense to be initiated by the possible momentary interlude between the front wheel being powered by first and second gear, as I would expect this type of effect to be most noticable while in an unpowered state. He mentioned all this because he said that side car set ups run similar off set loads, and are particularly prone to episodes of tank slapping.
So I'll throw a block under the rear axle and spin the tires to check for resistance after checking the tire pressures.
Admittedly quite a long shot.
But almost easier to check than to argue about.