Genuine AP Master cylinder with plastic tank.
The master cylinder is the heart of any hydraulic system and the hardest to troubleshoot. A pedal that can be slowly pushed to the floor indicates the master cylinder is worn. Fluid dripping off either the brake or clutch pedal is a sure sign that the respective master cylinder is leaking. Brake and clutch masters look similar, later models have plastic reservoirs, and they are NOT interchangable because they are different internally. Ensure the correct DOT4 or DOT5.1 fluid is used. At 0.70" bore size the original all metal master cylinder is available as
GMC171ORIGINAL or
GMC172 for larger capacity type for Cooper S.
BRAKE MASTER HAS LARGE MOUNTING FOOT, CLUTCH MASTER HAS SMALLER MOUNTING FOOT.
Ensure the correct DOT4 or DOT5.1 brake fluid is used as these cylinders are not designed to use anything else such as Castrol SRF for racing or any mineral fluid.