If you drive a vehicle with a manual transmission, it has both a clutch master cylinder and a slave cylinder. The master cylinder is where clutch fluid is stored. When you push the clutch pedal,clutch fluid flows from the master cylinder to the slave cylinder, producing the required pressure to move the clutch. The master cylinder has internal and external seals that can wear out over time. When internal seals fail, clutch fluid circulates inside the master cylinder instead of going to the slave cylinder. When internal seals fail, the master cylinder can leak clutch fluid, causing the clutch to malfunction. You may even see clutc fluid inside the car down by the clutch pedal. Other symptoms of master cylinder deterioration include your clutch pedal going all the way to the floor and an inability to change gears.