Pin hole in cast iron head

Is there any access to the back side of the pinhole through the water passage? If there was, I'd try flooding the area with a thinned epoxy. You wouldn't need much to cover the hole and the material would be pushed against the wall by the water pressure. Should never leak. If I had to weld/braze it, I'd try blobbing some silicon bronze rod over that area with either oxy/acetylene or TIG. I recently repaired a broken cast iron part with a steel weldment to replace the missing parts. I used silicon bronze rod and TIG to join the steel parts to the original cast iron and with a bit of preheat and slow cooling, I was able to keep it from fracturing. The rod flowed well and doesn't require flux.