I'm also pondering this as I'm nearing 74k miles and only a bit over 2k are mine. On other vehicles I have not been lucky with flushes but the X5's ZF is an entirely different transmission. I'm definitely going to change the fluid and filter.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim