Cooling system leak

I just replaced the water pump on my car. It no longer leaks from the pump nor leak fluid while running. Prior to replacing the pump I noticed a whistling sound from the right (if sitting in the car, left if standing in front) head/valve cover/manifold from what appears to be some type of sensor. Coolant is gushing from it but I do not know what it is. I was thinking the engine cooling temperature sensor (ECT), but I cannot seem to find the location of what I am sure is a sensor online. One site talked about the ECT being on the right head but I, forgive me for not knowing as I can get by on certain repairs but am no mechanic, do not know from which perspective right/left is. There is what appears to be a rubber housed plug that goes over the sensor, which is located on top of the head between the valve cover and intake manifold. It is not a fluid line. It is at the rear of the head on the left (facing engine from radiator side) and leaks terribly. Please help me.