Your problem is not necessarily hydraulic. It could be mechanical. In the old days when lots and lots of American cars had manuals, you would see what you describe from time to time.

In extreme cases the diaphragm is pushed past center and stays disengaged. I'm not saying that this is your problem, but it is likely. You need to push in the clutch where the pedal stays down and then rock the car to see if the clutch is decoupled. If it is release the hydraulic pressure in some way and see if it stays decoupled. If it does then the problem is mechanical.

Good luck,