As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
OIL DRAIN VALVE WAS REMOVED BECAUSE OF LEAK, UPON REMOVAL IT WAS DISCOVERED THAT SMALL NUT HOLDING SLUDGE VALVE ASSY TOGETHER WAS WORE TO MIN AMOUNT AND MISSING ONE HALF, IF NUT HAD COME OFF VALVE ASSY WOULD OPEN CAUSING ENGINE OIL TO COMPLETLY DRAIN.