Avan,
The Onan engines are used many other places. As this is the case, if your local Onan guy won't take it on for little or no cost, then find a local small engine shop that will admit that they know about Onan engines and cultivate a relationship.
When you do that, ask him what the engine is....
He will say that it is a "QG" or some such. Write that down. When you ever again have to talk to someone about say that you have a Onan QG Microquiet and any small engine guy will know where he is starting with the thing.
Matt