I just ordered a litre of ATF fluid and two crush washers from my local dealer.
They said there are various types of ATF fluid for the e90 and using my chassis number they have the right oil, they also said it has no spec details on it to cross reference it with castrol or Mobil etc
1 ltr oil = £9
Two washers = £0.34
A litre of castrol was over £10 delivered so it's a no brainier really head down to the dealers for the right gear!