Per BMW, these fluids are life-long, but I would like to change them once in a while...
4.0 Oil Change Intervals
Maintenance requirements per the vehicle’s Service Booklet or the respective Service Maintenance Checklist.
Replacement final drives: same as for new vehicles.
All models as of 9/97 production are factory-filled with synthetic rear axle oil having a long-life service rating.
No oil changes are required for the life of the vehicle.
2011 E92 M3 DCT
1991 Spec Miata
2008 E92 M3 DCT
2008 E92 M3 6MT
2008 E92 335xi