Mine (2001) came with a 5.5 GENERAC. Only one major problem,a crankshaft oil seal blew out...oil all over the place. Had a shop remove, rebuild and reinstall. Around 2300 bucks. HOWEVER....during Sandy, I started it up and with an extension cord nightmare, the genny provided lights and TV and the fridge for 4 straight days. It RAN for 4 straight days! (The motorhomes' 75 gallon gas tank..recently filled, helped out too!)
Reading here on the Forum, either GENERAC or ONAN...both are good, both have problems. And...btw, parts for GENERAC are available. Dealers seem really far and few between, so any major work...find a good shop.