Just for reference I'll post up some of the information I found when researching whether Dexron VI was now appropriate for the GM 5L40E tranny. As some may have already discovered, Cadillac uses the 5L40E transmission in some of the 1999-? CTS models and GM says Dexron VI is now appropriate for them as it is backwards compatible with the Dexron III original fill.
What many folks dont know is that just because GM chose the same name for the BMW/CTS transmissions (5L40E) doesnt mean that they are the exact same transmission. Refer to the attachments for the specific examples.
What I was never able to conclude with taking the specific differences into account is whether the Dex VI would then indeed be recomended by GM for the BMW 5L40E. More than likely it would be just fine (As BMW has superceded the original ETL-8072 part # with a Dexron VI part #) but would it be preferred to the original fill? That is the question.*Note: I ended up going with the Castrol Import Multivehichle ATF for my fill and drain refill cycles as it meets the ETL-8072b spec.
Obviously we can obsess about this to no end but as Starless has shown -- For peice of mind you can not go wrong with what was put in there originally.
The next question will be what do for peice of mind when we can no longer get the original fill anywhere?