Id ask what their process is on looking for the cracks and what equipment they used to check. Because where your cracks are located, you cant see that mount when you car is on a hoist (you can only see the 2 rear mounts). You can ONLY see the front 2 mounts with a cavity camera. - Try catching them out?
You said you took your car to BMW where they found the cracks? If so ask him (the BMW Dealer) if he is willing to sign a piece of paper that states that in his "X" amount of years of experience as a BMW Dealer/Mechanic, it would be impossible for these cracks to appear within the km's travelled. And that he has dealt and has vast experience with subframe issues before.
Last edited by Honro; 11-23-2012 at 02:21 AM.