Well, idk about you but i leave mine outside. (pretty much wanting to fuck someone up for testing my gangster attempting to steal it from me). If you dont shut the valve that holds pressure in the cylinder, moisture gets in there and fucks the seals up. If the ram isn't fully seated, the top seal can get fucked up because of surface rust on the ram. The little chrome ram below the handle can do that too.
A "friend's" lift did that too because they had an engine suspended with it for a few months in the garage. it's not climate controlled. Ram got some corrosion on it and now it will drop on its own SLOWLY and takes forever to jack up. Zero evidence of a fluid leak.
Harbor freight DOES sell rams you could probably fit somehow. Idk. I just remembered seeing them thinking that was cool in case you needed to pull a frame or build your own press or back hoe or something. As far as rebuilding rams i can't help ya there. My inner pussy says "replace it". Hope you get it fixed. Pulling/moving engines around without one is a bitch. I've done it, would never go back to it if i could help it.