I broke my boom at the same place (the vang attachement) during the 2006 Key West Race Week. We found a local weld shop to weld it back together. It was welded all around at the break and then an 8" long piece of angle iron was welded along the top and another along the bottom.
This worked for two reasons: One is because the main is loose footed. Second, since we take the main off after every race we had already cut a notch in the boom sail track about 3 ft back from the outboard end. The slot is just big enough to fit the car that attaches to the main clew.
We sailed with that boom for a whole season while we waited for a new one. It wasn't pretty but it worked just fine. That old boom has been laying around the club for a couple of years, unfortunately, it appears that someone finally threw it out.
