1999 Cobra Sierra

AFTER ~20 MILES OF STOP-AND-GO DRIVING, BRAKED AT ~40 MPH TO SLOW/STOP FOR TRAFFIC 5- TO 6 CAR-LENGTHS AHEAD. BRAKE PEDAL SANK TO FLOOR WITH LITTLE RESISTANCE, NO SLOWING OF VEHICLE. DURING BODY REPAIRS, SHOP EMPLOYEE NOTED "SPONGY" BRAKE PEDAL FEEL, `INEFFECTIVE DURING HARD BRAKING'. TRUCK TRANSFERRED TO MECHANIC, WHO FOUND BRAKE MASTER CYLINDER LEAKING FROM REAR SEAL & RESERVOIR GASKETS - AND ALSO FOUND ALL FRONT PADS WORN `TO THE POINT OF NEEDING REPLACEMENT'. SELLING GM DEALER REPLACED PADS BUT DENIED M/C LEAKAGE, BUT SECOND DEALER (DUTTON GMC IN RIVERSIDE, CA) CONFIRMED LEAKAGE AND REPLACED M/C UNDER WARRANTY. 2,100 MILES LATER, ON 10/4/99, NOTED FRESH FLUID LEAKAGE AT REAR OF M/C; WHEN CAP REMOVED, NEW FLUID HAD TURNED VERY DARK; WHEN REPLACING CAP, NOTED FLUID "SQUISHING" FROM ROUND SEALS BETWEEN RESERVOIR AND M/C BORE.