What was found
PHX - AIR TURNBACK - FLT 0001 - ON CLIMBOUT FROM PHX EN ROUTE TO ORD LT ENGINE OIL PRESSURE INDICATED 300 PSI, AIRCRAFT TURNED BACK TO PHX. MAINTENANCE TROUBLESHOT THE HIGH OIL PRESSURE INDICATION PER AWA ER 26-7920-02091-KL1, THE DIFFERENTIAL PRESSURE TRANSDUCER WAS REPLACED FOR TROUBLESHOOTING BUT THE READINGS REMAINED THE SAME AS ORIGINAL TRANSDUCER. A SMALL LEAK WAS NOTED AT THE LT ENGINE DE-OILER OUTLET AND A CARBON SEAL WAS REPLACED TO STOP THE LEAK. AS A PRECAUTIONARY MEASURE THE LT ENGINE NR 4 SCAVENGE VALVE WAS REPLACED IAW AMM 79-23-51-401. OIL PRESSURE WITHIN LIMITS PER AMM 71-00-00-991-155A.