Think you will find a knack to this, GOOGLE will bring a plethora to the mind.
Did mine once when I found fluid was low. The grub screw closes the path to a pin hole somewhere on the body of the cylinder from which the fluid will jet out at high speed when the grub screw is released/pedal depressed. WEAR EYE PROTECTION if you do it. Turns out I had a leaky slave so I replaced it all with a new sealed system from Jeep. That was in the days before I knew of birtys/lighthouse/rockauto etc. I believe you can get slave and masters seperately from the likes of RA rather than a whole sealed unit.What is the fluid level like? if it's low you probably have a leak. Master I think leaks into the foot well, slave into the bell housing. The OEM system does not have exposure to air as there is a rubber seal under the cap. The only thing that would really affect the fluid condition is heat as far as I can see.