THE ACFT WAS EN ROUTE FROM FLIN FLON AIRPORT, MANITOBA, CD, TO MASON CITY, IA, AND HAD STOPPED AT GRAND FORKS, ND, FOR FUEL AND TO CLEAR CUSTOMS. DURING TAXI FOR TAKEOFF, THE ACFT STRUCK A 1-INCH CONCRETE LIP ON THE RAMP AND THE RIGHT MAIN LANDING GEAR COLLAPSED. POST ACCIDENT EXAMINATION REVEALED THE ACTUATOR ROD END WAS BENT AND ONE OF FOUR SPRINGS ON THE OVERCENTER CAM DEVICE WAS DETACHED FROM ITS PROPER ATTACH POINT AND WAS EXCESSIVELY STRETCHED. WITH THE ACFT ON JACKS THE SPRING WAS REATTACHED AND THE GEAR WAS EXTENDED, TRAPPING THE SPRING BETWEEN THE DOWNLOCK SWITCH AND THE DOWNLOCK OVERCENTER MECHANISM. WITH SOME WEIGHT APPLIED TO THE LANDING GEAR, A FIRM UPWARD PRESSURE WAS APPLIED TO THE OVERCENTER DEVICE AND THE RIGHT MAIN LANDING GEAR RETRACTED. FURTHER TESTS REVEALED THAT THE LANDING GEAR SELECTOR HANDLE DID NOT ALWAYS CATCH THE SAFETY LATCH WHEN PLACED IN THE NEUTRAL POSITION, AND THAT IT WAS POSSIBLE FOR THE SELECTOR TO GO FROM DOWN TO UP WITHOUT TRIGGERING THE LATCH.