Thanks all for your interest and insight: I have not accessed and inspected the starter or stator. Does anyone have schematics or a repair manual I could follow?
I would like to summarize my issue again, holistically:
Battery had been getting weaker requiring a charge after a couple failed starts and then would start and operate. This went on for maybe 15-20 different day/rides and in retrospect has progressively got worse. Kinda similar to my road bike 1050 Tiger now that I think about it. Except the Tiger is still starting.
Anyhow, this last ride with the Sherco, the engine stopped while riding mid-high revs in 5th gear (AFTER starting and warming up). I coasted to a stop with the dead engine. Switched ignition on/off and then tried the starter, and it fired up and operated as usual. The next day this happened again; BUT after 1hr of solid riding. Trying to start it now it behaves differently each time. Sometimes just a click. Sometimes a very laboured and slow try - like something is resisting it. Voltage meter shows a complete drop from 14v to zero when it only clicks. And drops slower when it’s a laboured try.
I’ve connected to an external battery source. When it only clicks it actually draws the external battery source (boosting with a car) so low, the head lights dim.
While playing around with this, the bike did start and run shortly twice. The first time: a laboured start led to 10 seconds of running and then died. The second time the start was normal (not laboured!) and ran good for 30 seconds and then died.
Any way to test the Voltage regulator?
And how best to access and inspect the stator and starter?