What's the best fluid to use? I see a lot of posts saying they just use Dexron III but I would like to know there is a BMW-specific fluid that I should be using. For all I know, the previous owner could have put domestic tranny fluid in it.

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Current:
2001 BMW X5, 4.4i, 138K miles, Black & Tan.

Past:
1984 318i
1993 318i
1993 325i
2001 325i
1997 528i
1974 Porsche 911 2.7
1976 Porsche 911s
1978 Porsche 911 Targa
1985 Porsche 924
1987 Porsche 944 S2 Cabrio