Start - you can definitely do the transmission fluid yourself. I have an '06 X5 3.0 Automatic. The fluid is Dexron VI, commonly available. I chose to go with Valvoline. I did the drain, pan drop, filter replacement (OE BMW), and filled with fresh fluid (~6qts IIRC). Given that you can't get all the fluid out in one shot, I drove around with it for about 2 weeks then did a drain and fill with some more fluid. The objective there was to dilute the remaining fluid with fresh fluid and then put in some more fresh fluid. Been driving that way for 35K miles now and no issues.

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2006 X5 3.0L - Schwarz Black/Truffle Brown
Stock
But I keep it clean