Clutch Cylinder Haunted!

Master cylinder can have "residual check valve" that will allow the fluid to flow back as long there is a strong spring pushing the actuator back. nominally ~10 psig in the line

Is the clutch master cylinder pushrod length too long? When the clutch pedal returns to the resting position (clutch engaged), does the piston in the master cylinder return all the way back into the resting position within the master cylinder?

David; Combination of the two previous posts. Strong spring should push the fluid from slave cylinder back to master; however, you state it is impossible to push slave piston back. If your stainless line is replacing the original line, what happens if you should loosen the line where it is connected under the chassis near the cross member? (Hate squirting brake fluid) Should you relieve the pressure at that point, I would suggest the master cylinder is building pressure with each "pump" of the clutch pedal and not allowing fluid to return.
You stated you also replaced the master. Not familiar with your specific application (correct application?), but are there any adjustments with the rod from the clutch pedal to the master cylinder piston. It appears the piston in the master cylinder is not returning to the point to permit the return of fluid.

Make sure when the piston in the slave is totally retracted, the rod ( adjustable actuating rod ) should almost be loose, the book calls for a measurement of 3 1/8 as a approximate length of the rod, if it is adjusted all the way out it will not retract fully and that's what your describing.