As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT ENGINE WAS LOSING RPM. WHEN RPM GOT BELOW 2000 THE PILOT FEATHERED THE ENGINE AND LANDED SAFELY. AT ENGINE TEAR DOWN THE NR 5 CYLINDER EXHAUST SEAT HAD COME LOOSE IN THE HEAD AND CAUSE ALUMINUM SHAVINGS TO GET IN THE OIL SYSTEM AND BLOCK THE PROP GOVERNOR. PROBABLE CAUSE WAS A SUDDEN COOL DOWN OF THE ENGINE AT SOME POINT.