Just an owner of a 193k-mile, regularly-tracked 128i passing through
Sorry about your issues OP. It's kinda the risk we run driving hard around tracks. If you do swap for a used motor, I'd get one and start working on things like oil pan baffling, better bearings, and any other internal issue you can think of. I'd also think about doing all the usual gaskets. You know, while you're in there
Maybe you'd consider swapping to a 128i. Same suspension and everything, just less powerful and more reliable...