If the valve is not leaking coolant , you can test the operation by running the engine up to temperature with the heater on , feel the hose temperature, then switch to max A/C , at which time the valve will close and in a couple of mins. the temperature of one hose at least will drop ; due to lack of coolant circulation.
If the valve is operational , then use silicone sealant over the cracks , to prevent road spray intrusion.