I have a 2012 3.5 EB with 280K miles. Been running great but saw coolant under it when parked. Dealer advised it's coolant that went through the engine and leaked out the exhaust. 5 of 6 cylinders show coolant entered. Been running great. No milky oil. No white smoke. Not overheating. Power and mileage is normal. Has been well cared for and is otherwise in excellent condition. Oil stays brown between changes. What options might I have? Does this engine need to be replaced?