I've used IR thermometer to identify hotspots, temperature spikes etc...if the body of the generator is 100°F after 30 minutes of operation, but the bearing area is 200°, then ya got something to inspect...same goes for the VR, wiring, engine head, engine block, radiator, etc...
I've used IR thermometer to identify malfunctioning relays in an automated hardwood kiln operation...going through their control system, we were able to identify faulty yet functioning components, measure amp draws before and after component replacement, and show that energy saved paid for the replacements in less than a year...on another project, I found a faulty splice in a circuit that was acting like a choke and causing the control system to react adversely to actual conditions, causing all kinds of problems...
I suggest taking that buggy out for a half-hour or so test drive, then back at base with engine idling, take IR thermometer readings of mechanical parts of generator, then electro-mechanical parts as suggested, then follow the charging circuit to the VR and battery, etc...don't forget your fire extinguisher for the test drive tho