A few months ago, I bought an '89 740T that had been catastrophically overheated. I paid so little for the car, I figured I would either do what was necessary to repair it, or part it out and make some profit.

Anyway, my mechanic and I judged that the affected engine parts weren't too far gone, and we've spent our spare time in the last several weeks rebuilding.

Last night, all of this effort culminated in turning the key for the first time, following correct procedures for the first start to be sure oil gets to all the right places.

Anyway, when we reconnected the distributor, and turned the key, and the car started right up. Great, right?

Well, there's a problem. When we originally removed the head (weeks ago), one of the exhaust manifold studs broke (of course; not uncommon). When the machine shop milled the head, the guy also drilled and re-tapped that hole to accept a bolt of a slightly larger diameter. This wouldn't have been a problem, but he drilled too far into the hole, and penetrated the water jacket. Now there's a coolant leak from around the new exhaust manifold bolt.

Is there a way to successfully and reliably repair this and seal the leak, or is the head toast?

Thanks in advance.