Shifting on 1993 Honda Civic del Sol

3 weeks ago, when I started my car it made this noise. Boyfriend said it sounded like the hydraulic fluid was empty. Sure enough, it was. Refilled it. Car was fine for 3 days. Then began NOT wanting to shift. My dad bled the line of the hydraulic fluid. Car drove fine again for a week. Then no shifting once again. I had the master cylinder replaced and for 4 days, it worked awesome. Now it's back to NOT shifting again. Anyone know what I should try next? I paid $150.00 for a master cylinder when evidently I didn't need one. Thank you. The hydraulic fluid is NOT empty, it has remained full since I filled it a few weeks ago...

The clutch has two hydraulic components a clutch master cylinder which when you press the clutch pedal generates pressure and transmits this pressure through a hollow steel line to the clutch slave cylinder which in turn operates the clutch fork disengaging the power from the engine from reaching the gearbox. Look and see if after replacing ther clutch master cylinder if the fluid level is still OK if not you may have fluid loss from the pipe where it goes into the clutch master cylinder or from the clutch slave cylinder itself. The same contaminated fluid that caused the clutch master cylinder to fail was also circulating through the system into the clutch slave cylinder and may have damaged it internally. As one person presses the clutch pedal have another person look at the slave cylinder to see that it has "full travel" and look for signs of fluid leakage.