As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) HEATER RUNNING RICHER AND LEAVING A HEAVIER THAN NORMAL EXHAUST DEPOSIT ON THE FUSELAGE IN-FLIGHT. ON GROUND, IT WOULD BLOW OUT CARBON DEPOSIT FROM THE EXHAUST STACK AND EXHAUST DARKER THAN NORMAL DECAY TEST CARRIED OUT. HEATER WAS FACTORY REMANUFACTURED WITH EXTENDED LIFE COMBUSTION TUBE.