I have an older model Bosch Aquastar 1600 tankless water heater. Recently the water valve has started leaking, it appears water is coming out, just dripping, where the shaft from the gas valve moves back and forth. I took it apart, there is a diaphragm in there, but I don't see any holes in it. Does anyone have any ideas as to what is causing the drip? It drips slowly when the water is off, but much quicker when water is going through the heater. Is there a repair kit available for this?