JP, Colins web site gives good advice. I also use brass or copper plugs, but after cleaning the holes and I mean very clean, I put a little Permatex Gold on my finger and wipe a very small amount around the seat edges. I've never had a plug leak yet doing it that way. Once the plugs are seated, wipe any excess sealer off. Older blocks can get tiny imperfections around the seat area and the perminent sealer fills them. PJ