?
As far as im aware, they put in a new oversize cylinder, along with new seals. This costs about $270 from memory, but you need to wait for it to be done, then have the master cylinder put back in.
Or, do as i said, go buy a $70 new one. Two bolts inside the engine bay on the cylinder, and one clip on top of the clutch pedal. Not a hard task at all.
Never replace something worn out with second hand sheit. Asking for more trouble later....