Stripped drain plug hole

[dev6315]

Hey guys. Question. When I was winterizing this past fall, one of my brass drain plugs on the starboard side of the block is just about stripped. Obviously not the plug, but the block. It does grab just a bit, and did not leak a drop of antifreeze over the winter. I personally don't trust leaving it this way for the water. What is my best coarse of action? Heli-coil, drill and tap, etc?
If it were a normal bolt hole I know it would be easy, but with needing to keep a passage for drainage is my concern. Any insight is appreciated. I figured this has happened to someone before as I'm sure it's a pretty common occurrence on older cast blocks. Thank you!

 

[Bt Doctur]

repair is best done with the engine out of the boat and on a stand.
if the plug was 1/4 inch, try retapping the block to be sure the threads are still there, might get a reducer for a 1/8 plug.another option is to try a metric size plug.
if it was 1/8 already,could try a metric sized plug and retap block.

 

[dev6315]

It is a 1/4" plug now. I guess I will try a metric sized plug. Is drilling larger and using a heli-coil or re-tapping a no-no? Also, how much pressure is on that plug while running? I know its in a cooling passage, but am I making too big of a deal out of this???
BT doctur, thanks for the ideas.