According to theOwners Manual for the E71 X6 there is no dipstick fitted, and this has worried or annoyed more than a few Owners who possibly like me have a healthy mistrust of computer systems and like to see 'real oil' on a 'real dipstick'.
Well there's some good news for the 40d, and possible other variant owners of the E70 too - there is one!! On the E71 X6 40d it is to the right side of the engine at the back of the bay. As per the images below. I can only assume it is to allow the BMW Service folks to fill the cars back up after a oil and filter change without needing to faff about with the iDrive. Confirmed by my dealer.....



Hope it's of use to others.............