My 10HDKCA genset has a coolant leak at the recovery tank where the plastic fitting for the rubber hose mounts to at the bottom of the tank. According to local Onan distributor they remove plastic fitting and replace with brass fitting(sealing with pipe tape). Use care not to split tank by making fitting overly tight. Be sure to refill radiator to proper level as a leak at recovery tank will cause coolant loss each time genset is run and shut down.
2007 Mountain Aire 4528