what is the liquid is in it

That is the oil that helps cool the coil. Specifically, what kind of oil it is, I don't know. If it's the style of Mallory coil I'm thinking, it has a top held on with 4 screws. Those screws have "O" rings.

I would try refilling it if you can figure out what oil you need. May not work but you are only out a couple bucks if it doesn't.

But I'm one of those guys that tries to fix something before I go for a replacement.