My leak turned out to be a rogue nail (misplaced by the installer in 2012). This is one of the reasons I don't like air nailers that can be fired by simply pushing the point down while holding the trigger. A little wobble, bump your elbow, whatever, and you have a nail that's nowhere near it's intended destination. I prefer the ones that have to be pressed down, pull the trigger, and release the trigger before firing it again. But they're slower. Roofers don't do slow. They did my roof in ONE DAY, start to finish.
I went on the roof with the insurance adjusters Thursday, and we found of small blob of adhesive sealant that had apparently hardened and cracked with 11 summers and winters of exposure. The sealant was just peeking out from under the edge of a shingle about 4 feet down from the ridge, and not really visible from the ground. The nail head was visible below the bottom edge and right at the joint of two shingles in the row above, meaning water was being funneled straight at the nail. I removed the dried out sealant and pulled the nail out with my fingernails and then plugged the hole with some asphalt/fiberglass caulk. I also put some in the groove between the two shingles above, as well as under the edges to glue them back down. I had to lift 'em a little to properly access the hole for patching. I THINK I got it sealed up.
We had a pretty heavy and sustained rain early this morning, so after the missus got up, I had another little attic crawl and took a better/closer look at what's been going on. Apparently, the leak has been active for a while according to the stain on the attic side of the decking and some delamination of the plywood. There's also a water stain on a nearby rafter where water ran down the top of it (but didn't drip off the rafter) before the plywood delaminated and sagged enough to just let it drip straight down. The delamination probably also lifted the underlayment and the edge of the shingle enough to slow the water even more. The leak was just not bad enough until now (obviously it had to wait until the ceiling was painted and finished, right?). From what I could see this morning, it's drying up. The cool damp weather isn't letting it dry very fast, but a few days in the 70's with sun on the roof, it should be dry as a bone up there again.
@Donoroto , I do have a ridge vent, but there is zero evidence that even a single drop has come in through that, even after 11+ years of service. I had it added to mitigate some of the risk of the roof lifting during a lesser tornado, and actually expected to see more dripping up there than I do. There isn't a single water stain on the rafters, the edge of the sheathing, nor even a mark in the dust that's been accumulating since 1975. I also have eave vents at the west end of the house, and on the NE and SW sides of the house where the T-shaped roof has two gables. The soffits are all vented as well. Dunno why or how, but water simply doesn't go in the vent. Now that we've had that discussion, though ....... The small energy savings in the summer was just a bonus, with the primary reason being to prevent the roof from coming off in a storm it should be able to survive. Wind damage mitigation was the initial purpose of ridge vents, not energy savings. Someone just noticed a slight decrease in their summer power bill. I did so many other things that autumn that it would be hard for me to say what had the greatest energy impact. New/better textured roof (apparently better radiant heat refraction), ridge vent. larger gable vents, new double pane windows, fiberglass entry doors, new siding with R10 underlayment, not to mention sealing up a lotta leaks (bad door seals, etc). Unfortunately, looks like crappy workmanship is about to push me back outside to catch up with failing materials that were improperly installed.