K-Seal. About $16.00 for an 8oz bottle. Does not matter if you have antifreeze or not in the system.

Had a cracked head or bad head gasket one on our 96 New Yorker. Put that in three years ago with the engine blowing coolant out the fill cap.

Three years later it still runs and not blowing coolant.

I've used it on some other problems for a cheap fix and it has held up.

Worth a try.