34 coolant leak

[ctvpa]

Greetings. I have a 34 V8 with the water pumps located at the front of the head.
I can lose half gallon in 10 miles. I have checked the overflow, and it is not overwhelming the radiator.
I have used dye, removed the plugs, and pressurized the cooling system, with no leak. I did that for more than 2 weeks, changing the position of the pistons every other day.
It starts and runs fine. Nothing leaking anywhere. I have equal pressure in each cylinder.
When not running, I do not lose a drop.
I have changed the head gasket twice. No coolant is in the oil. The radiator tests positive for Monoxide. I just cannot find it. Any ideas?

Also, does anyone know of any cast heads available?
Thanks