good point. most simple thing to check is the starter. pull the seat and the tank. take a 5mm allens and pull the starter cover. I can't remember if you can actually see where it engages. If not, you may just want to pull the starter altogether--still not a big job.
To find out if it's the engine or the gearbox. pull the gearbox back like you were doing a spline lube--enough so that the splines are out of the clutch. try to spin the gearbox with the kickstart and try to spin the engine using a 6mm allens in the nose of the crank behind the alternator cover.
I'm eager to find out what's the dealieyo.