Dennis, the fasteners in cars like BMW's are often completely specific to the application, are sometimes unusual threads and sizes, and can have specific strength requirements. I hate to say it but taking a bolt that has already failed out of a front suspension upright, retapping to SAE and stuffing in a grade 8 SAE fastener is, to me, an unacceptable repair on a street car. Knowing if it's a adequate repair would mean figuring out what the loads are and why the original bolt failed. If you think about it, the bolt is going through a hole in a thing, and being threaded into another thing. What if the fit of the bolt shank in the thing is critical? If it's a steering arm, maybe it is...
Brian