Maybe you call it something else, but that's the best description I could come up with. The slave is physically linked to the clutch basket by a pair of push rods, one short..one long, with a steel ball between them. This passes thru the engine from one side to the other in a "push rod channel".... Perhaps tube would have been a better term?? It's possible for DOT3 to leak past a bad slave piston seal and also leak past the tube seal that the rods pass thru. I thought you must have, but have you ever rebuilt a complete clutch system???