Had an overheat alarm on one of a pair of 6LP 315's yesterday. Dumped the coolant in the bilge. Looked like it could be from a pin hole in the exhaust manifold which is apparently reasonably common, but after pulling that off we could see that there is a hole in the rear of the head through to the water jacket. Has anyone ever come across this and come up with a solution that doesn't involve a new head?