I've done a drain/replace filter/fill on a 2004 3.0 GM trans at 45k and just did the same on a 2003 4.6is ZF with 40k.

Both shifted fine before the change. Both had dark fluid and magnets coated with gray stuff. No chunks of anything in the pan though, thankfully.

Seeing the condition of the fluid at that mileage I would definitely not follow the lifetime recommendation.

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04 X5 3.0i auto
03 X5 4.6is