A tank is a tank, whether it's plastic or metal. (The tank would be the portions of the radiator (top and bottom) where the hoses attach.) A radiator shop can reseal a leaking tank, if that's what you want. In my opinion, that's not ususally a cost effective option when dealing with a presumably 30 year-old radiator. But you would need to talk to a convenient radiator shop to make an informed decision.