As you know, Onan is a Cummins product. Cummins has 30+ "Coach Care Centers". They obviously have the Onan knowledge, parts and service. My experience with the Coach Care system was good.
There is one at 10088 S. 136Th Street, Omaha, NE. 402-551-7678
Another is at 8201 Ne Parvin Road, Kansas City, MO. 816-414-8200
Also 450 W Northtown Road, Normal, IL. 309-452-4454