The Bars leak pellets work extremely well. GM had a bulletin on using them because of casting porosity issues. I had a pair of ported iron heads that magnafluxing showed cracks and the did leak. I would use the bars leak pellets and the leak would stop and we would race all season. My cracks were in the exhaust ports so no problems in that area. However the poster here should try to see how far up the leak is. If it gets by the rings when the piston is down it is just a time bomb as the cylinder pressures being high may not let the stuff seal. I would use them as a precaution as you do not want coolant in the oil.