Do not put oil in this system.It uses brake fluid in the reservoir.If the system doesn't have any fluid in it, there is a leak, and both the clutch master cyl and the clutch slave should be replaced. They both were used the same amount of times, and wear evenly. When you add fluid, the clutch master cyl compresses the fluid down the line/hose into the clutch slave cyl. This depresses the clutch fork/arm and disengages the clutch disc so the input shaft into the transmission stops moving, allowing the trans to be put into gear. LOOK FOR THE FLUID LEAKING TO ISOLATE THE PROBLEM. This is a closed system, and the fluid never gets used, unless there is a leak.

You need to add hydraulic oil (DOT 3 brake fluid) and bleed the clutch line. Bleed the line just as you would a brake line. There should be a nipple you can loosen that looks just like the ones in the brake system. Simply pump 3 - 5 times hold pedal, loosen bleeder screw until fluid comes out, tighten bleeder screw, the release clutch pedal. Do this until the fluid coming out of the bleeder screw is a solid stream and the pedal feels firm (as it would during normal operation).

Either the seal is bad on the clutch slave cylinder, or the line between the master cylinder and the slave cylinder is broken ,rubbed through, or punctured. Most likely it is the slave cylinder and will need to be replaced.