Well, I did the J-B Weld repair. I Used the original J-B Weld, carefully mixed it 50/50, cleaned the area with CRC brake cleaner and shop towel, sanded with coarse (40-grit) emery sandpaper with J-grade backing, and then cleaned it again with CRC brake cleaner. It was very hard as it was quite out of reach. Then I waited for 24+ hours for it to cure.
It looks like the leak wasn't from the aluminum but the bolt hole for the water outlet. Either the gasket repair didn't work perfectly or there is too much corrosion at the mating surfaces, especially near the bolt holes.
Anyway, the leak seems very small. It could come to less than a quart in 30,000 miles. So, I'll just keep an eye on the coolant (Toyota Long Life Red) level for now.
Perhaps I should just cover the bolt hole with adhesive silicone to see if it stops the seep.