Organbuilder,
I saw the picture you posted of the crack. It appears to be right smack dab at the bottom of the water jacket. The petcock drains the water jacket, but remember, this could be a swamp of goop and rust. I would try to cook as much moisture out of the crack area as I could with a small torch. It will probably boil the water and gunk on the other side of the crack.
Stuart
