Small Engine Troubleshooting Problems? Ask a Mechanic Now.
That all depends on what exactly is wrong with it.
Is it burning oil or leaking oil?
Leaking oil may be as simple as a bad gasket somewhere, or a bad welch plug. It may be as serious as a cracked block.
Burning oil may be as simple as a worn valve seal. It may also be as serious as a scratched cylinder wall.
You need to determine what is causing the loss of oil, and get an estimate on repair.
This is likely a BG or NH series unit. They were some of the toughest units that Onan has ever made. Other than being a little loud, none of the newer units have anything on this one. I'd much rather stick money into a BG or NH series than have a brand new HGJ.