The water in my home was shut off for five months while I was overseas. The heat was left on, set to about 60ð F. About 18 hours after turning the water back on, I noticed water stains forming on the ceiling beneath two adjacent second floor bathrooms (I estimate at least 2 pints had leaked out). There was no visible water anywhere in the bathrooms themselves. I shut the water off to those bathrooms, and when I got time about a week later turned it back and tried to track down the leak.

I drilled some holes in the ceiling to try to find the source with an inspection camera, but could find nothing. Tried running plenty of water through all the drains and toilets - still bone dry. The water to the bathrooms has been back on for over 48 hours and not a drop.

The stains cover a large area along a drywall seam, and don't help me track down the source. The only explanation I can think of it that a shower valve leaked behind a wall for a while, then stopped.

Is this plausible? I've attached a picture of the suspect valve (Delta - model unknown). If this is a likely culprit, can it be repaired (or am I better off replacing to ensure it doesn't happen again?)