I Would advise caution using additives in a higher mileage gearbox. Well any gearbox actually as you will be masking a potentially worsening problem that will inevitably bite you in the rear at the most in-opportune moment.

The flush and fill may be the better option and ensure you change out the filter but beware that this could also push more crud through the ports and channels in the valve plate than they can handle.

Try the basics first. Get someone to scan it and highlight any stored codes then do the soft reset (Throttle pedal down for 30 secs etc) or reset the adaptation values via PC (INPA/GT1/DIS)

Speaking from experience it isn't that hard to strip & rebuild the gearbox if you are methodical but is not something to take lightly.
However it has really rejuvenated mine and feels like a new car again.

__________________
Insanity is a state of mind, But which state is it????

If somethings are meant to be easy, you can trust in me to complicate matters significantly.


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2003 X5 3.0D Sport Auto.
1998 525 TDS SE Touring