340 exhaust manifold studs leaks coolant

1968 Barracuda 340 block
My passenger side exhaust stud located in the head leaks coolant. Just got the car running and noticed that the exhaust manifold had a small hole. So I remove the manfold to repair and noticed some liquid on the threads on the far back stud ( eight bank ) off the head that holds the manifold. I removed the stud and coolant started to flow out. The studs are stock and don't know if someone drilled to retap and went to deep into the passage? Is this proper that the stud is also used as a plug for the coolant passage. If so what needs to be done. Silicone on the threads or is it something else. Have no idea?

AAWJ 360 Heads
3671587-10

Thanks,
Chris