I change my oil every 7,500 miles. It is synthetic and it will not break down like conventional oils. But oil gets dirty and all you are doing is moving metal particles and dirt all on your bearings and such. As far as tranny and rear diff. I will be doing that when the car turns 30k. It is also good to flush your radiator once every two years. I will be doing mine this coming fall. BMW doesn't flush radiators, they call it lifetime fill.
'09 E92 ///M3 Interlagos Blue, 6MT
, Silver Novillo Leather, CF Trim, Premium Package, Technology Package, Cold Weather Package, Premium Sound, 19" Wheels, Moonroof-Toy/ '11 E90 328i
Black Saphire Metallic, Premium Package, Technology Package - Daily Driver '02 Nissan Xterra- Daily Driver/ '04 Yamaha R1
-Toy/ '06 Yamaha Raptor 350