Here's what BMW MEANS by "lifetime fill"

[Warren N.CA]

It means the diff and tranny are not likely to fail using the same oil before 100K. This is the mileage at which the CPO warranty expires, thereby (in BMW's view) terminating the useful life of the car. So, "lifetime" refers to the period during which BMW may have financial responsibility for the car.

[NoSpeedLimits]

That satement helps to explain why the tech at the local stealer recommended changing the trans fluid at 100K. Thanks.

[Mr Project]

That reminds me of certain products that are guaranteed 'for the life of the product'. Soooo, when it dies, that's the end of it's life, and no more warranty! :)