If you have old clutch master/slave, I would recommend swapping both.
FR Nabco Tokico Clutch Master Cylinder Nissan 240SX
FR Nabco Tokico Clutch Slave Cylinder Nissan 240SX
Mine died on me in heavy traffic.
Pedal stuck to the floor and I couldn't shift out of gear.
Coasted off the freeway far enough to get off a street.
Swap them both and be worry free.