replace it first, then bleed all 4 brake lines,starting at the farthest from teh master cylinder, and flush them WELL
if you dont use at least 2 small bottles of brake fluid you didnt flush completely, if youll do this every 2 yeasr youll never have to replace a master cylinder,caliper, or rear brake cylinder
OzarkJeep
77 CJ5, in a bunch of sanded and primered pieces