What was found
LEFT MAIN LANDING GEAR COLLAPSED AFTER LANDING, THEN ROLLING OUT 2000' AT THE START OF A RIGHT TURN ONTO A TAXIWAY. WHEN AIRCRAFT WAS JACKED FOR TESTING, THE GEAR WOULD RELEASE FROM EITHER THE UP/LOCKED OR DOWN/LOCKED POSITION BUT WOULD NOT CONTINUE TO THE POSITION COMMANDED. THERE APPEARED TO BE PRESSURE BECAUSE THE GEAR WOULD MOVE MANUALLY, BUT NOT AS EASY AS WHEN NOT PRESSURIZED. WE ASSUMED THERE WAS HYDRAULIC BYPASS IN THE GEAR ACTUATOR, BUT WHEN IT WAS REMOVED, WE FOUND THE MLG PIVOT ASSEMBLY SPLINE SHEARED JUST BEFORE THE SECTOR GEAR WHICH GOES INTO THE MAIN ACTUATOR. I CAN PROVIDE DIAGRAMS FOR LOCATION AND TYPE (CORROSION) OF FAILURE