As others have said you have to change both filter and haldex oil, every 60.000 km AFAIK.
I can't remember the code for the filter, but the oil one is
G 055 175 A2.
You will need ~900ml, so one bottle should be enough.
When doing the operation the oil which needs to be drained has to have a certain temperature but I can't remember how much exactly.
That's why I'd recommend doing the job with someone who knows what they are doing and has the proper tools (drain lines, VCDS for oil temperature measurement, etc).
Good luck!