Well, good news for a change. It was in fact the rear right brake cylinder spewing fluid at an alarming rate. However, I was doing some work in the garage and happened to glance over at the rear axle assembly that I removed from my parts car (and was too heavy to drag up to the attic) and lo and behold, the cylinders were still mounted! For some reason I had convinced myself that Ernie had pulled them (like he did the front calipers) before selling me the car, but there they were.

Pulled the right rear cylinder, took it apart and cleaned it up just to be safe, and swapped it out with Ms. J’s faulty one. After a quick power bleed, I can stop again! This parts car is starting to look like the best investment I’ve made in a long time.