Advice needed: How to repair Hudson bumper jack?

tinsled

I was fortunate to get the original Hudson bumper jack (less the handle) with my 1954 Hornet.

Only the jack will not move, looks like the little piston which is probably supposed to pump the oil to the big lifting piston is stuck. I am able to move the main rod of the lifting piston up-down when the valve in the foot is screwed open, but the little piston (pointed by arrow in the photo) is frozen... Also the bleeding screw (?) in the foot is frozen. Which way to take the jack apart for service without breaking any parts?

How do I take this apart for service & cleaning?