This is how you should check the current fluid level:
1) Vehicle level
2) Start engine
3) Press brake pedal to floor and shift through all gears several times at idle speed. Then shift to ”P” position.
4) Ensure trans oil temp 30-50 C. For best results, fluid should be at 30 C. An accurate level check is not possible if fluid temp rises above 50 C.
5) Undo oil filler plug
6) A small stream of fluid should flow out of the fill hole. If not, top up oil, Close the fill plug, Repeat from step # 3
7) Close the fill plug
8) Done!

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.