I worked at a local BMW dealer during college many years ago and recall seeing a high number of 740 and 540 cars come through requiring new engine blocks because of the the block/liner material. Don't recall the specifics but I think it had to do with a low (or maybe high) silicon content in the casting/liner. Something about the cylinder bores wore out due to the material used. Owners got a new engine block from BMW at no cost. The X5 wasn't out yet so I never saw those vehicles while working there.