I think that the broke off piece will make little difference. On a high hp vehicle the bell housing could fail. Better to get another block/engine. By the way, I worked exclusively on BMW for 25 years in dealerships and independent shops. I saw more bad work (and fixed it) at dealerships , than at independent shops. Also there are 2 alignment dowels to keep the trans input shaft in alignment on BMW’s at the bottom of the block. If that was broken off the trans… bad deal. Shitty manager and tech.