[Excaliber]

Some of these slaves must have a very powerful spring inside them? An internal spring will indeed push on the fork until the throw out bearing stops that action by contacting the pressure plate fingers. Normally a modest external return spring, properly affixed, is enough to overcome both the internal spring AND force the hydraulic fluid out of the slave, up the line and back into the master cylinder. A restriction in the return of the fluid to the master cylinder, therefore, would also have to be a consideration in this scenario.

The ERA uses a BMW slave, I have had mine apart. That spring isn't very strong, it's quite mild in fact. But it's strong enough to slowly push the slave piston forward and the throw out bearing against the P.P., which is why I run a return spring and an adjustable rod to set the allowed clearance of the throw out.