The Onan - Cummins manual gives a few other things like spark plug and air filter replacement. If you don't have a manual you can download it from their website.
Another example, the manual for our 4000 watt gasoline generator says to remove the plugs from the bottom of the muffler and run it under load to blow the carbon out. I don't remember the hours.
They recommend removing the head and scraping carbon off at 500 hours. That could be a pain.
2011 Sunseeker 3100
1997 Pathfinder Toad