I recently was flushing my coolant from my G37. Flush went fine, but in the process of screwing the drain plug back in it broke from the thread piece. Thread piece became stuck. So I decided to gut out the remaining piece of the plug. In the process of me doing so I created a small in hole at the top of the drain extension. Radiator doesn't hold coolant do to the leakage from the small hole. I've replaced the drain plug but as far as the hole on top the only thing I could thing of was to seal it with JB Weld Extreme Heat Metallic Paste. It's done it's job so far, but the paste wears off eventually. Is there any other methods I can use to seal the small hole.

Marine Tex is another superior and extreme epoxy ,using a true 5 - 1 ratio mix , for boats , can take that temp there by a radiator easily .
Future consideration - Try what I do , I like too loosen a lower hose to drain , or in the case with my juke there is a "split" lower hose with a 3" plastic coupling under middle of radiator - I broke that loose to drain. EVER since radiators became plastic junk ?? I try to never use those weak , foolish drain-caulck valves.
Unless there is a real good reason , OR if I have got to one early-on( like first 4 or 5 years from new ) and it's not 'frozen' , AND I've coated with some very thick silicone grease when done to be easier the 3 years later I flush again

p.s. site doesn't like c***........drain-c*** .......anybody ????