A883 2nd & 3rd question
Quoting direct from Factory Service Manual:
1.Linkage Interference
2.Gearshift Rods out of adjustment.
3. Second or direct speed gear synchronizer clutch teeth worn.
4. Clutch linkage bore or face out of alignment.
two things they didn't mention there were a worn gear/shaft surface and interlock teeth on the gears themselves.
A gear that is loose on it's shaft can wiggle around and cause the gear to jump out.
Also there are little angled teeth on the gears that interlock into the slide rings that basically force it to stay in place under a load.
When these get worn the angle changes on these teeth to where they actuall force the gear away instead of holding it locked in place.
A redo for sure and possibly even a new gear or two and a shaft.
Note the angles at the ends of the teeth on this slider ring?
The slider and the gear itself have these, and are what causes the gear to stay in.
When those angles get worn down they allow the gear to be forced out of the ring and this is what you feel at the shifter when it jumps out of gear.
Not say this is all it is by any means, but it does need to be checked while it's open and they are looking at why it jumps out.
Worn shift Forks
slider teeth
gear teeth
Friction surfaces condition (gears, rings and shafts)
Bushings and bearings
These are the most common causes of jumping out of gear.
I exagerated the angled section on one of the teeth with the two red lines so you can see how it works.
The ring and gear both have these so that they interlock once in position.