Brazing has always been the acceptable way to repair cast iron breakage. The only time it does not take well is when the surface is not prepared properly or the iron is left cold while the brazing is done. In 1957, I accidentally shot through the floorboard of my Dad's new 1957 Ford pickup. The bullet shattered the exhaust manifold and blew fragments through the radiator. We built the manifold back up by breaking up cast iron watering bowls (for the cows) and brazed the pieces into the manifold until it was sealed. That truck ran for years without any other manifold problems. I personally would not spend the effort to fix a cracked exhaust now unless it was an emergency. The junk yards are full of them.

Regards,
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Will Dallas, www.willdallas.us, www.willdallas.org, www.willdallas.com, www.dallasprecision.com 86 245 DL 222K miles, 93 940 260K miles, 88 765 GLE 152K miles, 88 780 246K miles