It sounds to me, like a false netural (light on, but slightly in gear). Or a bad sidestand switch.
Sticking clutch plates would not make a difference if the bike was in netural.
I'm also missing somthing here. All nuts and bolts should have
been checked at the 600 mi service.
Loose mirror mounts, and steering bearings are almost normal.
Maybe a bit late for you but hopefully good for somebody seeing it, but I found a spark plug socket at Sears, 5/8", the hex top is (ta-da!) 19mm.
Better buy a socket with a 3/4 hex if your looking for 19MM.