Having the same problem with a new 1996 resto I picked up. Never had any problems with any of the other ZX7R's slave cylinder's I have worked on.
Seems it had a leak, and someone decided to epoxy or glue the body to the mount. No external corrosion.
Tried Deep Creep, Marvel pen oil, WD-40 pen fluid. No go. And if I break out the torch, it will melt the surrounding paint and require refinishing.
If you figure out another method let me know!