Found it. A bad intermediate servo.
This one was the hardest to remove. The snap ring notches are tough to get to when they're at the top. After I oiled up the ring and slid it around to where I could see the notches things got a lot easier.
Here's the intermediate servo. The smaller overdrive servo was OK but I'll be replacing that too.
I used the broken off piston to check the bores. The intermediate bore seemed pretty tight.
I'll guess at a couple thousands horizontally and a little more vertically. The overdrive side was slightly tighter.
A few pictures to help out the next victim.