I have a ISL 8.9L 400HP Cummins in a 2008 Forest River Charleston. The Diesel has a rear mounted radiator. I pull a 18' V nose enclosed trailer with auto in it and I started having overheating problems from Flagstaff to Amarillo . I had the water pump and thermostat changed and it was good until I left Texas in December heading to Florida. I had a mechanic to come over to the RV Park here in Port Charlotte FL and he said the Fan Clutch was bad and the Fan just freewheels and does not engage. His cost (plus 20% mu) is $1200. Is this a reasonable price?