We run nearly every day at this time of year for charging batteries and usually it is a 2 hour run. Around 300 hours annually.
After checking crankcase oil frequently for a couple of years, I do not check very often any more, as no oil add has been required between changes. I just look around for leaks and figure if there are none, them I am good to go. Oil changes at 250 hours reveal a full sump, little oil usage.
Linkages get oiled once in a while (a vague schedule!) but never seem to really need it, as the whole engine always has a light oil film. The gen set lives under a shed roof, but outside in a damp environment, and there is never a rust problem
Valve gear.......the pushrod and tappet cups are oiled only when there is no oil in them.......probably an average of once a week (say 12 hours run time)
I do squirt the rockers, rocker shaft, and top of the valves before every run, that put oil into the valve guide sumps.
After 1200 hours, it is all operating smoothly. I have had other issues, but lubrication is not one of them. These are very forgiving engines and the stresses are not great with the slow speed and only 6 HP output!
Cheers,
Hugh