my 94 ford ranger was fine then all the sudden the clutch went out. It wont go into gear and when you try and put it in reverse it grinds really loud. i have replaced the master cylinder three times and the slave cylinder twice. The fluid was gone and i put fluid back in it and it started working fine but today the gears are out but the resavoir is still full of fluid. What can be causing this issue? why does the clutch keep going out?