What was found
PILOT REPORTED LOW OIL PRESSURE WARNING SOUNDED LEFT ENGINE, AND GAUGE INDICATED ZERO OIL PRESSURE AT APPROXIMATELY 'GEAR-UP' TIME OF TAKEOFF. LANDING WITHOUT INCIDENT. TROUBLESHOOTING DETERMINED TO BE FROZEN BREATHER. THIS SYSTEM HAS AIR/OIL SEPARATOR. PIPER IS IN PROCESS OF MODIFYING SYSTEM. ALL OPERATORS OF SENECA V AIRCRAFT SHOULD C/W THIS MODIFICATION WHEN AVAILABLE. ROUTING OF LT ENGINE BREATHER IS SLIGHTLY DIFFERENT THAN RT DUE TO AIR CONDITIONING COMPRESSOR BEING MOUNTED ON LT ENGINE. A LARGE PUDDLE OF OIL WAS FOUND AT LOCATION OF GROUND RUN. OIL WAS BLOWN THROUGH RETURN HOSE FROM SEPARATOR TO ENGINE.