What was found
AFTER TAKEOFF; DOOR NOT LATCHED, LIGHT REMAINED ON; COMPLETED PROPER CHECKLIST AND UNABLE TO HAVE SATISFACTORY UPLATCH CHECKLIST; HAD TO DUMB FUEL AND RETURN TO STATION. ACCOMPLISHED GEAR SWING FOR TROUBLESHOT; FABRICATED DOOR ASSEMBLY AND PERFORMED GEAR SWING OPERATIONAL CHECK NORMAL AS PER DC-8 M/M 12-81-1 AND M/M 32-10-0. REMOVED AND REPLACED FROZEN BEARING IN LT MAIN LANDING GEAR DOOR UPLATCH MECHANISM IN ACCORDANCE WITH M/M 32-31-4. OPERATIONAL CHECK NORMAL. ALSO FOUND LOOSE TARGET ON RT SIDE MAIN LANDING GEAR DOOR UPLATCH SWITCH, TIGHTENED IN ACCORDANCE WITH M/M 32-36-0; OPERATIONAL CHECK NORMAL.