What was found
AIRCRAFT RETURNED TO PLATFORM AS A CONSEQUENCE OF DURING LEFT ENGINE START, THE STARTER VALVE LIGHT TURNED ON AND EICAS MESSAGES, L ENG STARTED. DISPLAYED WITH START SELECTOR IN GND, ENGINE FAILED TO ROTATE. THE BREAKERS WERE RESEATED AND THE LEFT ENGINE WAS STARTED IN MANUAL MODE, BEING CORRECT. THE REPORT WAS DEFERRED IAW MEL 80-00-2. DURING OVERNIGHT CHECK, THE LEFT START VALVE WAS REPLACED IAW MM 80-11-02, TESTED CORRECT. DEFERRED REPORT WAS CLOSED.