Most work would involve removing the generator from the RV.
Typically dropping the generator doesn't require exceptional or specialized skill, but it is a good bit of labor. You need to disconnect the connections to the generator (12V power, ground, 120V AC output, and fuel), and then unbolt the generator from its mount on the RV and lower it down with e.g. a car floor jack or transmission jack. Sometimes it's necessary to park the RV on ramps or jack it up to get clearance under the side skirt.
The Onan 4KY series of 4000W generators weighs around 175 pounds. Yours is likely a little lighter, but it's still a good bit to manage safely without a jack of some sort. These units are not designed to be portable!
At any rate, if you're somewhat handy, it's certainly not beyond the realm of possibility to drop and reinstall the generator yourself and save that part of the cost of diagnosis/repair.