Do not take crap,
if you baught the car from BMW pre-owned, and they are stating that crap, tell them that they sold you a motor vehicle with undisclosed faults, and that they need to prove that you actually had the shoddy repairs done, tell them that they sold you a car that was not as per BMW pre-owned terms and conditions, and that you will hold them liable for the full purchase value.
Mention things like the NCA, automotive onbudsman, tell them you are going to contact the bank and lodge an appeal to have the finance application cancelled based on the "break in the truet relationship between yourself and BMW where you were sold a vehilce that was not as per the BMW pre-owned promise"
Watch how quickly they do backflips to sort you out, be a serious doos here, cause if your not... you will get screwed.
By the way, that heat forming process that I spoke about originally, I am damm sure thats what happened here, inconsistancy in the cast.
And over time, it will break.
That crank should of been manafactured to withstand the maximum torque that the engine can deliver without incident. If they suspect that the engine has been abused, you should see wear on other parts as well, such as piston sleeves ect....
Hardball or walking funny... you choose.