As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT BLEED DUCT MASTER WARNING IN FLT, CREW ELECTED TO RTF AND DURING DESCENT WHILE PASSING THROUGH 15000 FEET THE CAPTAIN MANUALLY DEPLOYED THE 02 MASKS. MX RE-SECURED MT137 AND CLEANED MT138 RAN ENGINES OPS CHECKED 0, RE-SECURED MT137 AND CLEANED MT138 RAN ENGINES OPS CHECKED. MX FERRIED TO OKC FOR O2 GENERATOR REPLACEMENT REQUIRED BY MASK DEPLOYMENT.