L BRAKE FAILED ON TAXI AFTER LNDG.

Narrative

I WAS RETURNING FROM AN IFR TRAINING FLT TO ST. LOUIS DOWNTOWN-PARKS (CPS); WITH MY INSTRUCTOR. I WAS ON THE ILS APCH TO RWY 30L WHEN THE TWR DIRECTED ME TO CIRCLE R TO RWY 12L. THE WINDS WERE 180 DEGS AT 15 KTS. I MADE A NORMAL LNDG ON RWY 12L AND TAXIED TO THE END OF THE RWY AT ITS INTXN WITH TXWY M. AS I APCHED THAT INTXN; I APPLIED MY BRAKES TO SLOW THE ACFT BEFORE I TURNED R ONTO TXWY M. WHEN I APPLIED MY BRAKES; THE R BRAKE CAUGHT; BUT THE L BRAKE DID NOT. THE ACFT IMMEDIATELY AND SHARPLY TURNED TO THE R. THE NOSE GEAR DROPPED OFF THE EDGE RWY AND THE PROP CAME IN CONTACT WITH THE RWY AND GND. WHEN I EXITED THE ACFT; I OBSERVED THAT THE NOSE GEAR HAD SUNK SEVERAL INCHES INTO THE SOFT GND ALONGSIDE THE RWY AND STRUCK THE CONCRETE WHERE RWY 12L INTERSECTS WITH TXWY M. THE NOSE GEAR SHEARED OFF BELOW THE STRUT; CAUSING THE PROP TO STRIKE THE EDGE OF THE RWY AND GND. THE BRAKES WERE TESTED BY OWNER OF FBO WITH WITNESSES PRESENT. THE L BRAKE DID NOT WORK. IT IS BELIEVED THAT THE O-RING FAILED. I BELIEVE THIS ACCIDENT WAS A RESULT OF A MECHANICAL FAILURE TO THE L BRAKE AND THE LOCATION WHERE THE NOSE GEAR DROPPED OFF THE RWY.