Your car has a split-diagonal hydraulic system so each front brake works on a different part of the master cylinder. If both front brakes are locking up, the brake fluid isn't releasing back to the master cylinder. You can prove that when they're locked up by cracking open the bleeder screws. Even easier, loosen the lines at the master cylinder. If that makes the brakes release, the next time it happens, loosen the two nuts holding the master cylinder to the booster. If they release that way, you have the wrong push rod adjustment or the brake light switch is holding the brake pedal from fully releasing.
If cracking the lines open releases the brakes, suspect the brake fluid is contaminated with petroleum product such as engine oil, transmission fluid, or power steering fluid. That will cause the rubber lip seals in the master cylinder to swell and grow past the fluid return ports, blocking them off and keeping the brakes applied. The ONLY acceptable repair for that is to replace every part in the system that has a rubber part that contacts brake fluid, and you must flush and dry all of the steel lines. Thank goodness you don't have anti-lock brakes, but that will still be a very expensive repair. Ten days is about right for that contamination to affect your new master cylinder.
Sunday, August 14th, 2011 AT 9:07 PM