Great point.If you are going to press it out, it will pay to protect the hole in the end of the arbor.
More thoughts.... try pushing the cannon tube on further, to get it to start moving then the opposite way to remove... back and forth, if it starts to yield to this technique.
I had a rusty movement that would not come apart and I was playing around with the electrolysis method of derusting at the time and tried it on the movement, and it freed everything up. It only removes rust and does not damage brass or good steel. It did discolor the brass, but light I'm sure the stain would not be hard to remove.
One other extreme thought, would be to drill a couple of tiny holes in the wall of the cannon tube, to leach some substance of choice into the tube. It would not compromise the strength of the tube.