Usually the Onan 5500 is run with propane , and not really subject to gumming up like gasoline run generators. With that being said, the best thing he can do is run it periodically say once a month for a half hour or so. Mine is run on propane ,so I do the once a month
As far as his issue, sounds like an adjustment. As far as gumming up, is it a gas run generator ? If so then he needs to take some precaution, at the least shutting off the gas, and running it until it quits when not using it. If propane like I said just run it periodically .
