If you aren't worried about being a purist, you could put in a pull cable operated shut-off valve. This can be used in place of the Ranco valve, but without the leaking problem, and you will be able to completely shut off the water to the heater core in the summer from inside the cab. The Ranco valve in the wide open position still significantly restricts the flow of water to the heater core, so you will want to duplicate this somehow.
Carl
