And now the counterpoint:

There is no correlation between changing the fluid and the transmission lasting any longer. That's the bad news. The good news is that if you want to change it, just because you want to anyways, you are early enough that there are unlikely to be any ill effects of doing so.

Agree with Ard that you won't notice anything different after the change.

Since you are under warranty, I wouldn't let anyone but the BMW dealer do it. Don't give them a reason to put your warranty coverage in doubt. If you introduce a third party, you create additional risk. You won't be concealing the fact that the fluid was changed by using a third party, it won't be a secret later, so it comes down to who you can hold responsible if there is a problem. Better to have OTTC (One Throat to Choke)

Yes, it is expensive. So don't do it then. Or do it, because it gives you peace of mind. Your call. There isn't a right answer.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue