What was found
SEA - DURING TAKEOFF "L DOOR" LIGHT DID NOT GO OUT WITH GEAR UP, DURING CLIMB PASSING 10,000 FT THE DOOR CLOSED. CONTINUED FLIGHT AS NORMAL. USED ALT GEAR EXT FOR LANDING. FERRIED TO PDX FOR REPAIRS. DUPLICATED CONDITION WITH OPS CHECK OF GEAR PRIMARY EXTENSION AND RETRACTION SYSTEM IAW Q-400 AMM TASK 32-31-00-710-801, READ PSEU AND FOUND ALL APPLICABLE SENSORS READING NORMAL FOR GIVEN POSITION. NO FAULTS OCCURRED. REMOVED AND REPLACED NR 1 MLG DOOR SOLENOID SEQUENCE VALVE IAW Q-400 AMM TASKS 32-31-41-000-801 AND 32-31-41-400-801. OPS CHECK OF GEAR PRIMARY EXTENSION AND RETRACTION SYSTEM CHECKS GOOD IAW Q-400 TASK 32-31-00-710-801 15 TIMES, ALL INDICATIONS GOOD. LEAK CHECK OF NR 1 MLG DOOR SOLENOID SEQUENCE VALVE GOOD. RETURNED TO SERVICE.