I have 120K miles on my 03 4.6is and I am letting the trans fluid ride.

Same thing with my E38 740i, although that car has under 100K miles so I might consider doing a drain and refill on that one just to refresh the fluid a bit. Not sure it's worth it tho.

I did change the transfer case and front and rear diff fluids in my X5 at 100K miles just for yuks. Can't hurt to refresh those fluids - no such risk as in the case of an AT trans.

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2003 4.6is - SOLD
2003 M5 Imola
2008 Mini Cooper S
2011 Mazda CX9