Would you please explain what is a core exchange. I know that the fly wheel on the stock diff is welded, how can the dinan lsd be bolted in if the stock diff is welded in. If there is a solution to this I will spring for the dinan lsd. In the past I had changed out the stock diff on my 335i, but that was bolted on and the change was easily done and well worth it in performance. BMW is now welding their stock diff to stop this trend. Hope to hear your response. Thanks....