Hydraulic clutches for manual transmissions use brake fluid to supply ... Pushing in the clutch pedal makes fluid flow from a master cylinder (or fluid reservoir) to the slave cylinder, which ...

The brake fluid reservoir is usually plastic and clear or semi-translucent. This allows you to visualize the brake fluid ...

but like brake calipers, sometimes it can spring leaks or otherwise fail, and it must be rebuilt or replaced. The master cylinder is topped by the brake-fluid reservoir, which must be kept full.