As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT DEPARTED, PILOT NOTICED FLAMES FLICKERING THROUGH THE INSPECTION DOOR ON THE LEFT ENGINE AFTER REDUCING POWER, HE NOTED NO OIL PRESSURE AND SECURED THE ENGINE. THE AIRCRAFT RETURNED TO AIRPORT WITHOUT FURTHER INCIDENT. IT WAS DISCOVERED THAT CONVERTER KIT LW-13904D HAD BEEN INSTALLED SEVERAL HUNDRED HOURS PRIOR WITHOUT THE TECHNICIANS KNOWLEDGE OF THE REQUIREMENTS OF MSB 543A SUPP NR1 ENGINE IS RETIRED FROM SERVICE.