I just received a statement from my marina and was charged $620.00 for winterizing my twin 5.0 mercruisers which included an oil and filter change. Last fall I happen to be at the marina when my boat was being winterized and watched the process. The outdrives (2) were removed and the mechanic connected a hose from a 20 gallon drum of antifreeze to the water intake tube in the gimbal housing, started the engine and when the antifreeze started being pumped out of the exhaust he shut down the engine and proceeded to do the second engine. He then pump the motor oil out of the drip stick tube, changed the oil filter and install new engine oil. the total time was 45 minutes at a charge of $620.00. Does the charge sound about right ? Is the the correct method of winterizing the engine?: