I tested one of them with compressed air, it went very ineventful, the ram slowly moved until it reached end of its travel. Then I switched the side where I supplied air and it retracted. I tried that a few times, sometimes the ram would jump just a little, but nothing major. Of course I was careful and tried not to let in too much air at once. I used a ball valve for air.
I cannot open the second cylinder, it is plugged with aluminum plugs with a big allen wrench hole, I do not have a wrench for it. Will try penetrating oil PB Blaster and some vise grips.
i