After he did that, the area didn't leak again till tonight, when we got a moderate shower. Even the rain we got a few months back that caused flooding in parts of the area (including Uncle Barrett and Aunt Sybil's house), didn't produce a leak then.
Thinking the caulk finally gave up the ghost, so to speak, with the 100+ temperatures we've been having recently. This was the first "noticable" rain we've had here in over a month. Gunna see what can be done in the morning. The leak was dripping into the cats litter pan near the back door. Got one big clump of litter as a result.
I went outside with an umbrella and flashlight during the rain and determined no water was backing up from the gutter or the metal trough on the roof (which was one of mom's earlier theories), so it STILL has to be "shingle related" in my opinion.