I have a shut off valve immediately next to the pressure switch on the tank of my deep-well pump. Fir the third time in 20 years, it has started to leak from what appear to be perforations through the cast brass body of the valve. The first time I thought it must have been frozen and cracked so I replaced it. The next time it was obvious that it wasn't cracked and I thought maybe is was some strange galvanic reaction because of some steel fittings among the copper and brass, so I replaced it again. That was about 6 years ago. It has just started again to spray 3 or 4 fine streams of water from the top side of the valve. I'm game to replace it again, but can anybody explain why this keeps happening? See the pictures taken today.