IMHO… If the plug is rotted then it will need replacing.
Can you reach it an see if you can put your finger through it or a tool through it.
MAYBE, your call, try filling the hole with sealer where the plug is located and see if it stops the leak but usually there is too much grease for it to adhere to the metal; if you clean it up some, maybe.
Again, maybe sealant poured in the coolant will do something, but you are only playing games with it and the Freeze-Plug will win in the end.
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