It's been years since I have rebuilt a clutch master, since they have gotten so cheap, but if you really want to do this, first tear down the unit and lay all parts out in order to aid in reassembly. Next, inspect the bore of the unit to see how bad it is. It badly scratched or pitted, stop and replace the entire unit. If it looks ok, hone the bore with a hone tool using clean brake fluid, clean with more clean fluid, and install new parts using assembly lube. Bench bleed, then install and bleed the system.