cobbled brake system

Bad master meaning,With the vehicle stopped and engine idling;
A)if the system pumps up hard with multiple stroking, then drops; fluid is leaking past the piston seal and returning to the reservoir. A kit may cure this if the bore is usable, Or
B) if the system does not pump up hard, with multiple stroking, first prove the pushrod is allowing the pistons to return to the parked position, so the Compensating port can work.Then make sure there are pads in the rear calipers,lol. But
C) you can do all that and prove the MC is leaking internally, by process of elimination, or you can just rebuild/replace the master, and hope everybody, me included, is right,lol. .