After reading through dozens of posts on the topic, the consensus appears to be that a good quality Dexron VI ATF is the best choice. But I have a question - since you can't get anywhere near all of the oil out of the tranny during a flush, is there any possibility of incompatibility between the Dex VI and whatever fluid was put in the tranny at the factory (mine is a 2003 4.4 with 78K miles)? Thanks.

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT