BMW does not manufacture the transmission, ZF does. I do not believe BMW has "motive" other than to provide the highest level of technology available with regard to most major components of the vehicle especially the drivetrain. ZF engineers have evidently come to the conclusion that their product (and their good name) is well served by the recommendations they have published.

JCL's reference to the transmission as hydraulic system is spot on. And his message regarding its comparison to an engine is relevant and factual.

In industrial applications many OEM's continue to recommend drain intervals that are not relevant to today's superior performance fluids and most certainly do not pay attention to the reliability engineer's focus (and industries movement towards) condition based fluid change intervals as opposed to time or mileage based oil change intervals.

BMW/ ZF are I am sure, cognizant of the characteristics of the fluid as well as the dynamics of the wear mechanisms occurring in the transmission itself. In hydraulic systems especially, it is well known that particulates in the fluid damage system components and yet there are plenty of maintenance personnel who believe they are doing good by the machines they are responsible for by changing oil because it has achieved a certain length of service time, when in fact the opportunity to do more damage as JCL suggests, is real and in fact counterproductive to the machines life. Heavy equipment OEM's are well aware of this and ZF is a vendor to that market as well.

As far as the BMW/ZF transmission itself, the only improvement I would like to see would be an oil sampling valve somewhere on the transmission or its cooler lines. This valve (which would cost no more than $10.00) would enable monitoring of the fluid without opening the unit to the atmosphere. They are commonly installed on heavy equipment hydraulic systems, transmissions and many industrial hydraulic systems. Fluid degradation, contamination, viscosity, etc could easily be monitored and action could be taken as analysis results dictate.