47 coupe,
Confucius say: Rear Freeze plug leak because it hardest one to get to!
Seriously, if it's an original freeze plug (also called Core plug), 60 years is not a bad service life.
When you get the old plug out, clean the core hole in the block really well, before attempting to install a new one. I've always used a liberal swab of Permatex number 3 to ensure a good seal of core plugs. Worked for me since about '56!
If the core plug you're installing is the cup-type, you can use a socket and extension that will fit inside the cup flange then, holding it squarely against the hole, drive it in evenly.
If the plug is a expanding type, fit it into the hole, then expand it by hitting it dead center with a brass drift of about 3/4". One good whack with a one pound hammer should dimple it, causing it to expand and lock into the hole.
With good antifreeze in your cooling system, the new core plug should out-last you!
