Re: Master Cylinder?
Although more likely the master cylinder needs servicing (stainless sleeving and fitting an overhaul kit of rubber pieces, piston cups, springs etc etc) it could also be a leaking caliper seal. Check for fluid leaks at each wheel. Also check the rubber cover under the master cylinder cap is not upside down or damaged and that their is no crud or similar contaminates in the bottom of the master cylinder. A brake fluid bleed might also work; how long since the system was bled?