I have a small water leak and I mean small. While doing other work I cleaned the back of the head area we’re I thought the leak might be. Then I found this area on the block with a lot of corrosion and pitted real bad. Is this a plug from casting or machining and is that a water jacket area. Not wanting to open bigger can of worms but if it gets worse maybe I will have an idea of what I will have to do. Every time I get an answer to a question I find 3 more questions. As always thanks for the help , advice and encouragement this site provides.
Don't laugh at ths but if it were mine I would add cooling system sealer and not open a can of worms. The sealer like Barrs Leaks works well and will not plug-up the radiator core. After that I would keep an eye on it and perhaps you can avoid major surgery.
That looks like the steel core plug used to fill a casting hole. If it’s seeping it is rusted through and needs to be replaced. Likely when you remove it you will see how much sediment is blocking the water passages as well.