T stat housing won't seal

Using the helicoil you only have to drill out the manifold, tap it and insert the helicoil in the manifold. Original thermostat bolt can now be reused. Housing does not get drilled. It seems you want to take the easy way out and drill out the manifold and put next size up bolt. The guys here give their opinion on how the best way to correct the problem. You now have choices so do what you want.