BP Series II Knee Air Assist

I recently bought a BP Series II CNC with a 4HP 4J head. It has an air-assisted knee, but it's leaking air like a sieve out the top of the pedestal which then causes the z-axis servo-drive to fault and lower the knee. I found this post about replacing the Packing, Bottom Cover Seal, and Spring for a similar machine and bought those items, but when I get into the bottom of the pedestal, I don't see a snap ring or way to remove the plunger from the ball-screw. There are 4 screws, but they don't seem to release the plunger. I'm sure I'm just missing something stupid. Any ideas?

Here's a photo of the bottom of the pedestal with the cover and screws removed. The dark perimeter appears to be the leather packing, but I can't get it out.


Thanks.

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