The car is a 91 miata, just replaced the slave cylinder (to solve a slow leak) and the main problem still exists. If you press in the clutch and hold it for a few seconds there is no pressure when letting it out. If sitting with the car in gear and the clutch in after several seconds the car will start to creep. The system is very thoroughly bled (over a quart of fluid has passed through the system) and I'm led to believe that the master cylinder is the culprit. The part looks to be original as it has a nice coating of rust on it. Short of the clutch itself being bad this is the only part left. If you drive the car and shift quickly there are no problems, so I think that the internal seals are leaking and letting pressure out of the line.
