I have read on M3Forum that owners of this BMW CF strut tower brace have experienced the same failure. On my M3, the cast aluminum bracket atop the driver's side strut tower cracked where it mates up with the oval crossbar at the end of the bolted connection. So don't feel bad because you're not the only one who has experienced strut bar issues.
If I was in the market to buy replacement, I'd get a Mason Industries strut bar, or the one that Carbing makes, which is very shiny and purdy I might add, but it appears to be a 90% copy of the original Motorsport brace that came on my car so....meh. By default, the Mason bar wins my vote. There is another exception though, Dixis Spirit made a cool titanium strut brace that I would love to get my mits on.