My York oil furnace has an excess air reading of 3l% with fan OFF and 49% with fan ON. Other specs: draft .02-.04, smoke 0, CO2 9.1, efficiency 82%. Testo 327-1 combustion analyzer used . CO readings are: Fan OFF, 6ppm, 8ppm CO AirFree; Fan ON, 9ppm, 14ppm CO Airfree. My oil tech says EA fluctuation alone indicates possible cracked heat exchanger or leaking/warped gasket, furnace should be replaced. Two other independent techs did a visual and scope inspection, said furnace could be used safely. How important is the EA reading? The furnace is 25 years old, gently used in small house, no oil smell when coming on, no soot, no noise. Who do I believe? Thank you for your help.