ON this particular valve, the diaphragm should fail in the open position if it has a hole or a tear in it. In this case where you stated the valve failed in the closed position, or barely leaking any water, makes me believe it is clogged. Take out the solenoid and make sure all the passageways are not blocked with debris. BE CAREFUL, don't poke it too much, one of the holes has a diaphragm under it.
Do you have a well or is it municipal water?
Josh
Irrigation /Landscape Lighting / Pump and Well Specialist