BMW has designated the automatic transmission fluid in this vehicle as "lifetime fill", meaning it never is replaced during your standard servicing. This same ZF transmission recommends regular fluid changes in every other vehicle it is used in. BMW eventually conceded that premature transmission failure was a result of insufficient fluid replacement and recommended changing at least every 100,000 miles. More realistically, most BMW experts seem to agree replacing the fluid and the transmission pan containing the filter is best performed closer to every 60,000 miles to prevent premature failure.