yes it is true but it depends on where do you live ! Certain areas had more sulfur then others. I have seen many 540 and 740 and 840 engine replaced under warranty ! In Florida while the BMW specialist told me it was a bigger problem in the Norht-East coast. I'd just say keep it safe and try to get more proof that the engine has been replaced or there isn't any damage to the cylinder wall. Hard to find this failure because the car will run, just badly and most people will think it is something else not the engine ! (I had this problem) so make sure the engine is safe and sound and then it is true...