On Tuesday, the authorities pulled back the curtain on heating oil industrywide fraud that they said had festered for decades, despite promises by city officials over the years to clean up the trade.:In a city of glittering office towers and computerized transactions, the authorities say old-fashioned corruption of the most brazen kind still poisons the heating oil industry\. Drivers carry guns to guard their cash. Hidden paper records document fraudulent dealings, and then disappear by the end of the season. Deliverymen pump air into the fuel tanks of homes and municipal buildings, and use magnets to throw off the meters that are supposed to make sure oil is flowing through the hose, the authorities say.