Ok, I guess I deserved that opus.
It's one of the rears. The tread is nearly gone so I'm preparing for a new set of 4 in the "near" future. In the interest of further complicating things, while having the tires replaced I want to take the bare wheels back from the tire shop to strip and re-paint before the new rubber is mounted. In short, I decided to just live with the leak until I'm ready to do the whole tires and wheels job.