If it's Craftsman, it's a lifetime warranty. Have you brought it to the local Sears store?
I would NOT use a jack that is leaking. It's just begging for something to happen.
I have the same jack and totally love it. Have had it for 5+ years. I could lift my car or my truck totally off the ground with it if I could only balance it!
Bring it to Sears and see what they say, if they say no way, then either get a new one or try to find a repair place.