What was found
DURING CRUISE, THE LT HYD ENG PUMP AND LT ENG HYD OVERHEAT MESSAGES DISPLAYED AND THE PRESSURE LIGHT AND OVERHEAT LIGHT ILLUMINATED. AFTER 30 SECONDS THE OVERHEAT LIGHT WENT OUT, HYDRAULIC PRESSURE AND QUANTITY WERE NORMAL. THE ENGINE PUMP SWITCH WAS TURNED OFF. AFTER TEN MINUTES THE HYDRAULIC QUANTITY DECREASED AND THE LT HYD SYS PRESS MESSAGE AND LIGHT CAME ON. HYDRAULIC PRESSURE REMAINED NORMAL. WHEN FLAPS 1 DEGREE WAS SELECTED ON APPROACH, POWER XFER UNIT MESSAGE APPEARED AND THE LT HYDRAULIC PRESSURE WENT TO ZERO. ALTERNATE FLAP AND GEAR EXTENSION PROCEDURES WERE USED. AIRCRAFT LANDED WITHOUT INCIDENT. REPLACED THE LEFT ENGINE HYDRAULIC PUMP AND SYSTEM FILTERS. SYSTEM CHECK WAS NORMAL.