The slave cylinder actuates the clutch arm by use of hydraulic pressure.  Age and use wear this part out.  The first sign is a vague clutch, followed by leaking and eventually total failure.  This is a great thing to have around when your goes out, it is only a matter of time.  If your clutch is not as crisp as it used to be, go ahead and replace it or keep one in the glove box just in case.  This is a new, not rebuilt slave cylinder.  We have sold literally 100's of these with great success.  This part meets or exceeds OE spec.

This clutch slave cylinder fits the following: