Since I don't plan to repair this engine anyways, I liked your leak stop suggestion (though I'll be embarrassed to admit having used it 😂). I read some reviews and decided to put a bottle of Bar's Leaks 1109 Block Seal in it last night on the way home from work. It seemed to almost completely remedy the issue this morning. Some of the reviews stated that it took a few days to completely seal the leak, so I'll wait a bit before I update my original post.

I have high hopes that this will be a long term fix, since the leak is assumed to be in the manihead, which should have fairly low pressure in both the exhaust and coolant sides, unlike a bad head gasket leak into a cylinder.