Orca, sounds like you have a major bind somewhere in the system Could be at the cylinder, especially if it hasn't moved in a long while. Sounds dumb, but a sharp smack with a hammer on the end plate (where all 4 cables are) at the end of the piston. Somewhere it's jammed. CAUTION, if you DO free it with pressure in the system, it'll move! You don't want any of YOU in the way. Not uncommon for a piston to freeze up from disuse. Let us know.
Tree