[olddog]

What type of metal are the plugs made from? Aluminum has a very high coefficient of thermal expansion. This means the diameter of the hole changes every time the engine heats up and cools down. If the metal in the plug is not aluminum (which is doubtful) then the plug is not expanding and contracting with the aluminum. The sealant is not going to take that abuse.

I will check some tables at work tomorrow, but I’m thinking brass may be fairly close to aluminum, but you have to be careful mixing dissimilar metals.

A plug with a flange and an O-ring would be best if the block is flat for the flange to mate up to.

Last thought, tighten it while the engine is hot.