I rode to work the other day and my zx6-r developed a severe reluctance to change up,down or into neutral.
Luckily all I had to do was dismantle footrest/gearchange linkage and clean, polish and regrease it, and it was like new.
Thank christ I didn't have to dismantle the clutch/gearbox, as it was sounding like a return spring problem, which is internal.
Moral of the story.....Check the simple things first!