What was found
AFTER GEAR RETRACTION, EICAS MESSAGE, "GEAR DOOR" SYNOPTIC INDICATED LT MAIN GEAR DOOR NOT CLOSED, DUMPED FUEL AND RETURNED TO DEPARTURE. GROUND CHECK LOWER ACTUATOR; FLEX HOSES HAD NO PRESSURE UP. WING GEAR DOOR SEQUENCE VALVE REPLACED; RIGGED IAW MM 32-32-02-404-006, WING GEAR DOOR RETRACT ACTUATOR & OPS CHECKED NORMAL AND PERFORMED MLG RETRACTION TEST IAW MM 32-32-00; ALL NORMAL.