I have used the mechanically expanding copper plugs that are marketed by Dorman and NAPA with great success. There is also a rubber item that is very much prone to failure; should only be used in dire emergency. The expanding copper plugs are used in place of cup type core plugs and not the dish type that you hit with a hammer and ball end tool to seat. How about No. 1 Permatex to seal, just in case? Copper plugs in NAPA book are rated 3000 psi for copper plugs and 50 psi for rubber. I remember 200 psi for copper in Dorman catalog. NAPA catalog misprint? I think so. Carry rubber plugs for emergencies? Warren Anderson Sedona,AZ