As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DUCT PRESSURE SPLIT AT FLT LEVEL 350 IN CRUISE. NIS LEFT 87.7 RIGHT 87.7 PRESSURE LEFT 17 PSI RIGHT 42 PSI. ENGINE BLEEDS ON APU BLEED OFF. ISOLATION VALVE AUTO BOTH PACKS AUTO. PRESSURE THROUGHOUT CLIMB WAS L 12 R 42. FOUND PRSOV ON NR 1 ENGINE LEAKING AT BELLOWS SPLIT LINE IN CASE. REPLACED NR 1 ENGINE PRSOV. REPAIR CONFIRMATION GOOD.