It has been raining steadily here for the past sixteen hours or so. Most of the time, it has been moderate or heavy. Both DN and I have spent several minutes on multiple occasions underneath the chimney where the leak was, shining a flashlight onto the problem area. So far, it is as dry as a bone. No evidence of moisture, and certainly no falling droplets.
For the time being, I will deem it fixed. Grumpy is happy! At least about the roof, anyway.