OK, victory.
Pulled the footpeg, brake lever, clutch cable and adjuster cover, clutch cover, clutch basket and voila.
DPO had a spring on one of the idler arms installed incorrectly, putting way too much tension/pressure on the shifter drum assembly. Look at the spring at the base of the idler arm, upper left:
Closer:
Doesn't belong there. Belongs in front of that boss. Notice the witness marks from when it was installed correctly prior to DPO's fiddlings.
Notice also the wear on the top edge of the idler wheel at the end of that shaft from the excessive pressure from the few cycles it had post "rebuild". That long arm with the red assembly lube was also slightly bent, not sure if that was contributing or a result of having so much force applied to it. Quick press against the center of the span of that and it was straight enough, I didn't bother swapping my spare part.
Eric, one other thing - next time you reinstall a clutch, bend down one of these tabs on the locking washer so the clutch nut doesn't spin off and grenade.
Measured the clutch springs while they were out and naturally discovered that they are about 3mm under the service limit. Adding those to your tab Eric.
Tested the shifting with the spring in the proper position and it's working much better, although it has a tendency to catch false neutrals between 4th and 5th, but that could simply be because it's on the lift and not spinning nor under power. Not going to worry about that till it's back on the road. Put it all back together, put some oil in it and held my breath - yes the kickstarter shaft seal survived yet another installing-over, and everything is oil tight, including the shifter shaft seal I replaced in November. Moving on.
THANK YOU to all for the suggestions and whatnot, including my "Thirsty" pal Matt.