[Rich Biebel]

I'd fix the Onan if possible and skip the Generac. Or buy a new or used Onan if you could find one.

The only thing that could be plastic and break inside the generator end is the rotor. It has plastic fins on it where the windings were wound. If a piece broke off it could damage the stator. The outer part with windings....

Both parts are available and replaceable. If the rest of the unit was in decent shape....not a mess, and not need any other parts....it would be worth fixing and for a lot less that a new one.