For many years the ceiling of my family room has had a small, but annoying leak when it rains (but not every time it rains). I have a two-story house, but the family room is a one-story extension and has a flat roof. The location of the drip into the room changes from time to time, but it is always near the perimeter of the room. I don't know if the water originates on the flat roof (which has been coated with a rubber-based product over tar paper) or if it has travelled down behind the wood siding of the second story above it. I want to finally end the leak, but I don't know where to attack the problem. How do I find the source of the leak?