Trouble with engine hoist cylinder

I have my own engine hoist, as some of us do. It got to where when you pump the handle on the cylinder, it hardly moves up.

I checked the fluid level in the cylinder, and it started spilling out when I removed the plug. So I figure that my cylinder is worn out and buy another new cylinder about 2 months ago.

We pulled the engine/trans out of my son's Challenger and put the engine on a stand.

We drag the hoist up to the front garage to move an engine and trans together the other day, and the cylinder won't lift the engine only a little higher than a foot off the ground, then won't lift anymore. It's like the old cylinder again.

Can this be due to cold weather affecting the pressure inside the cylinder?

Why can't the new cylinder lift an engine already?

Any ideas?