G200 VEERED LEFT AFTER TOUCHDOWN; AND DIRECTIONAL CONTROL COULD NOT BE MAINTAINED BY RUDDER OR BRAKE APPLICATION. ACFT DEPARTED THE RWY.

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I WAS SIC AND PF OF A GULFSTREAM 200; THAT EXPERIENCED A RWY EXCURSION WHILE LNDG. VFR CONDITIONS EXISTED; WITH WINDS 33010. A VISUAL APCH BACKED UP BY THE ILS WAS CONDUCTED TO RWY 24. THE ACFT WAS STABILIZED THROUGHOUT ALL PHASES OF THE APCH TO TOUCHDOWN. NORMAL BRAKING WAS APPLIED AND THE ACFT VEERED L; I RELEASED THE L BRAKE AND APPLIED R RUDDER TRYING TO BRING THE ACFT BACK ON TRACK WITH NEGATIVE RESULTS. MORE R RUDDER AND R BRAKING WAS APPLIED; HOWEVER; THE ACFT CONTINUED ON ITS L TRACK. I THEN CALLED OUT FOR HELP AND SIMULTANEOUSLY FELT THE CAPT'S FEET ON THE R RUDDER AND R BRAKE; WHICH I HAD NOW PUSHED FULL TRAVEL. THE ACFT CONTINUED TO PULL L AND EXITED THE RWY. ONCE ON THE GRASS; WE WERE ABLE TO REGAIN DIRECTIONAL CTL USING THE RUDDER AND RETURNED THE ACFT TO THE RWY TO COMPLETE THE ROLLOUT. THRUST REVERSERS WERE NOT DEPLOYED; BECAUSE DIRECTIONAL CTL WAS THE PRIORITY IMMEDIATELY AFTER TOUCHDOWN. ALL SYS APPEARED TO BE WORKING AND THE ACFT WAS TAXIED TO PARKING. THE ACFT WAS INSPECTED AND DAMAGE TO THE R KRUGER FLAP; R FLAP AND PUNCTURE TO THE R WING LEADING EDGE ABOVE THE KRUGER FLAP WAS FOUND. INSPECTION OF THE RWY BY AN ARPT EMPLOYEE; FOUND THAT A TAXI SIGN HAD APPARENTLY BEEN HIT DURING THE DEV. AFTER MUCH THOUGHT I SUSPECT THAT THE L BRAKE FAILED TO RELEASE WHEN COMMANDED; HOWEVER I MUST STATE THAT THIS IS PURE SPECULATION. THE ACFT ALSO WAS VERY CLOSE TO MAX LNDG WT; REF WAS 140 KTS; WHICH UNDER NORMAL CONDITIONS WOULD NOT HAVE BEEN A PROB; HOWEVER; WT AND MOMENTUM WITH THE SUDDEN PULL TO THE L; MAY HAVE CONTRIBUTED TO THE LACK OF EFFECTIVE RUDDER CTL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT THERE WAS NO OBSTRUCTION TO RUDDER OR BRAKE PEDAL MOVEMENT WHILE THE PLTS WERE ATTEMPTING TO REGAIN CONTROL. MANUFACTURER'S INSPECTION REVEALED A BRAKE DEFECT ON THE ACFT. THE NOSE GEAR WAS FOUND TO BE OUT OF ALIGNMENT; ALTHOUGH THIS COULD HAVE BEEN CAUSED BY THE EXCURSION.