Rebuilt my 5hp24 (03, 4.4i) and now that I know what is in there, I have decided that I will replace the fluid every 30k miles. I can't think of any reason not to but a lot of reasons why I should.

Now, if only I could find the time to do my 4.8iS trans flush......

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2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.