How many hours on Onan Generator? Need help asap!

If you are using this as a commercial generator, I would suggest that since your income is related to it, I would go for a new one. If it is in an RV, then I would take the chance. First thing that I would ask the current owner is to allow me to have it load tested. Hire a company that does generator load testing to test the generator. They bring in a load bank and run the generator at maximum load. How long depends on you. It will show up quickly if the unit has a problem.