Found the leak

Some good news: After many weeks of putting up with five huge holes in the kitchen ceiling, while waiting unsuccessfully for the leak to re-occur, today our painter/friend and his drywaller/friend found a bunch of corrosion on a section of copper hot water pipe that was hiding between the holes. He sanded off the worst of the corrosion in one spot, and it started leaking immediately. A self-sealing (sort of) leak! Called a new plumber, and replaced the entire section.