As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT RETURNED TO DEN UNDER AMBER ALERT WITH THE LEFT ENGINE SHUT DOWN DUE TO AN OIL QUANTITY AND PRESSURE IRREGULARITY. *S/D* OIL QUANTITY WAS ZERO AND PRESSURE BELOW RED LINE AT START OF CRUISE. CAUSE WAS ATTRIBUTED TO PLASTIC SHIPPING CAP IN MAIN OIL PRESSURE TUBE. PRATT SERVICE BULLETIN PW4G-112-79-07 HAD JUST BEEN ACCOMPLISHED.