Freeze plug leaking

['65 chevy lover]

Just about ready to fire it up and BAM, got a leaking freeze plug on a brand new crate motor. I bought the motor in 2014 and, due to circumstances beyond my control, it has been sitting since then. Yesterday I filled the radiator and today, there was a puddle of fluid under it. After a bit of looking I determined it was coming from a freeze plug on the front of the motor. I called the engine builder and they said it could have happened because of the motor not being run since the 45 min break-in time they did. I'm not sure I agree with that. They told me to buy Blue Devil leak stop and that would fix it. Anyone here ever have problems like this with a new motor?