1988 Other Oldsmobile Models Head Gasket?

I own a 1988 Oldsmobile Regency 98. There is some sort of a leak in the engine which causes the radiator fluid to drain in a matter of minutes. The engine stays on when the car is idle but when I shift it to drive and let the engine run on its idle speed the engine shuts off. But if i hold the gas and keep driving, the car seems to drive perfectly fine as long as it doesn't come to a complete stop even though the radiator is all out of fluid. I got it looked at and one of the guys says that it might be a blown head gasket while the other one says it might be the water pump since its only losing water. What do you think it might be? and also if it is a head gasket would applying a sealant fix the problem?