Oil button diaphragm

[Austin in the Shed]

I am struggling to get mine to pieces. How do you remove the pressed in brass cap

Very carefully,The reason is when the bezel is screwed up its swages slightly the body around it.
The best way I found was to push the brass cap in slightly and with a scraper lightly dress the swaging off,hold the ebonite button in a 3 jaw chuck and pull carefully.
The brass washer that holds the spring behind the button is attached by a 5 Ba countersunk screw and it's easy to pull it out of the ebonite.