As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EN ROUTE TO CLD LEFT DUCT LEAK LIGHT ILLUMINATED. FOLLOWED QRH AND LIGHT DID NOT EXTINGUISH. SHUT DOWN LEFT ENGINE AND RETURNED TO LAX. RAN AIRCRAFT AND DUPLICATED DISCREPANCY. ISOLATED REGULATOR/RELIEF VALVE AS FAULTY. INSTALLED SERVICEABLE VALVE AND RAN AIRCRAFT EXTENSIVELY AT 100 PERCENT TQ. BLEEDS AUTO PACK NORMAL. NO DISCREPANCY OR DUCT LEAK LIGHT NOTED. OPS CHECKED GOOD.