Final answer:
The master cylinder of a hydraulic clutch system should be filled with brake fluid as per the manufacturer's specifications to ensure proper operation and avoid system damage.
Step-by-step explanation:
After bleeding the hydraulic clutch system, you would fill the master cylinder with brake fluid. It's important to use the specified fluid as recommended by the vehicle's manufacturer.
Using the wrong type of fluid, like transmission fluid, hydraulic fluid or anti-freeze could cause damage to the system. Brake fluid is designed to operate at high temperatures and under high pressure, which makes it suitable for use in hydraulic clutch systems.