As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI IN, NOTICED A DUCT PRESSURE SPLIT- RIGHT WAS @18 PSI - LEFT WAS AT 8 PSI. GROUNDED - YES. PERFORMED B737-900 AMM TASK 36-00-00-860-807. FOUND PRSOV LEAKING FROM MANUAL OVERRIDE NUT ON #1 ENGINE. REMOVED AND REPLACED PRSOV. OPS/LEAK CHECK GOOD. GROUND VERIFIED DUCT PRESSURES WITH IDLE RUN. REF AMM 36-11-04.