Quote from the almighty "bible"
The automatic transmission is not equipped with a dipstick. Checking the ATF (automatic transmission fluid) level requires measuring and maintaining a specified ATF temperature within a narrow range during the checking procedure. The checking temperature is not fully warm or cold (the ATF pan should be warm to the touch).
--Raise and safely support the vehicle to access the ATF plug.
--Warm up drivetrain by running engine until ATF reaaches specified temperature. Apply brake and, while idling engine, shift through all gears severeal times. Turn engine off.
--Connect vehicle to BMW diagnostic scan tool....
--Remove ATF fill plug (located on driver's side rear of tranny).
--Place transmission in neutral and restart engine.
--With ATF between 85-120degF, add fluid until it spills from fill hole.
--Reinstall fill plug using new sealing ring.
And that's how you check?! Damn. That's messed up.
And I don't get how your suppose to keep the car in neutral AND shift through all the gears. That just doesn't make sence.