You need to remove the leaking one and replace it with a new one. Some auto parts store sell ones that have a rubber bushing that you compress, to seal up the freeze plug hole. The metal ones, steel, or brass are the better way to go, but you almost need to pull the motor out to do it right in my opinion.
90 Comanche thing. Exo-cage, tube bed, with a few other things done Here is a link to some pics of it
If you have to ask why... Its a truggy thing and you wouldn't understand