start by checking the lines. if leaking, very easy fix. if lines are fine, buy master cylinder first- easy to change- cost 100. if still leaking buy slave cylinder- not near as easy to change- cost 120.
i had to replace mine on my 94yj. the master was like 90 bucks and the slave was an external so it wasnt hard to change and it cost like 70 bucks. i later found that it was just an o ring that was leakign air. whoops.