What was found
(CAN) THE LT MLG FWD DOOR WOULD NOT CLOSE WHEN GEAR SELECTED UP. (NO LT AMBER - NO LT GREEN) RT & NLG PERFORMED NORMALLY.VISUAL CONFIRMATION CONDUCTED THAT DOOR OPEN. GEAR CYCLED&DOOR REMAINED OPEN AGAIN. DECISION MADE TO RETURN.AN ALT EXTENSION CARRIED OUT & A/C LANDED W/O INCID. (NO CFR). MAINT CHANGED SEVERAL COMPONENTS FOR TROUBLESHOOTING PURPOSES BUT PROBLEM REMAINED. LT FWD MLG DO OR ACTUATOR FOUND TO BE CAUSE OF PROBLEM. COMPONENT CHANGED, WITH SEVERAL GEAR SWINGS CARRIED OUT&ALT EXTENSIONS COMPLETED. FUNCTION & LEAK CHECKED AS SERVICEABLE. A/C RETURNED TO SERVICE WITH NO FURTHER INCID.S TO RPT.