Blindly ripping things apart before a proper diagnosis is performed is a sure route to more problems / failure.

The proper route would have been to perform a leak down then you would have known for sure if there was a leak from combustion to coolant. This would have also identified the exact cylinder.

The leak area you have high lighted leads to a dowel pin and not coolant. It is possible that slight combustion gasses were making their way to the dowel pin but that isn't the cause of the overheat.