What was found
LANDING GEAR WOULD NOT EXTEND WHEN SELECTED. LANDING GEAR WAS MANUALLY EXTENDED TO FULL DOWN POSITION WITH 3 GREEN INDICATIONS. ON RETURN TO MX FACILITY, ACFT WAS PLACED ON JACKS AND LANDING GEAR FUNCTIONED NORMALLY. THIS PROBLEM OCCURRED APPROX 10 MONTH PREVIOUSLY. THE GEAR SELECTOR SWITCH WAS INSPECTED UPON REMOVAL AND SOME BURNING OR ARCING WAS EVIDENT ON THE SWITCH CONTACTS. IN ADDITION TO THE SELECTOR SWITCH BEING REPLACED THE CIRCUIT BREAKER, LANDING GEAR MOTOR AND MAIN GEAR DOWN SWITCH WERE ALSO REPLACED AS A PRECAUTION.