I HAVE REPLACED OLD GERBER SHOWER VALVES WITH NEW,AND THEY ARE STILL LEAKING.I REPLACED WITH NEW GERBER VALVES,NEW SEATS,MADE SURE THE WASHERS WERE IN PLACE,TIGHTENED PACKING NUT AND IT STILL IS DRIPPING.IS IT POSSIBLE I HAVE VALVES SWITCHED(HOT IN COLD AND VICE VERSA?)HELP