I pulled down only the driver's side headliner being careful to not take too much since I didn't have any glue to stick it back up. A-pillar looked great but with a bit more snooping I looked up toward the sunroof and.... Boom, I can see clearly to the light of day. Now, this may actually be normal with the sunroof open, I'm not sure, but this piqued my interest.
I climbed up, looked around, and found two black, plastic tabs. There's one on either side and I noticed one was facing fore and aft while the other was facing side to side. Both were cracked. I've got a full cage on top, so working on the sunroof was a real PITA, but I managed to get them off. Had to disconnect the wind guard first, raise up the spring tabs, and that was enough to get at the single Phillips head screw holding each down. I took them out and went to town with some super glue. I don't know if any of you have tried finding plastic epoxy (or any auto part for that matter) in Japan when you don't speak Japanese, but it's near impossible. Here's the tabs halfway through gluing.
After the next day, I reinstalled the tabs facing fore and aft and spent a few minutes drenching the top of my car with a hose, and NO LEAK!!!! Now, the real test is going to be making sure after a full night of rain nothing seeps in. I'll update you after that happens.
I know from searching the threads for cabin leaks that a lot of people have had a frustrating time with the sunroof, and hopefully this helps somebody out there