[Rick Parker]

Are these tapered pipe threads or straight threads with an "O" ring like a port plug used with AN fittings?

Coolant will seak out a leak before distilled water will. I have 1 1/4" taperd pipe plugs exactly like Boss 302 in my smallblock. I noticed some very minor leaking shortly after the initial build. I put in a pellet that I obtained from a GM dealer and it sealed the leakage, no leakage at all in several years. Later I found it is common practice at the dealerships for the techs to throw one or two in the cooling system after major teardowns to eliminate any minor leakage and reduce come backs.