Only ~18K on the '04 V8.
but it'll clear 19K on the way home this weekend. I haven't done anything but mod it since I picked it up in Feb of this year. I'll run through the fluids- transmission included- at 20K. It's been 7 years, so it's more about time than miles.
The '04 i6 had a few regulators (CPO), a water pump, alternator, and probably some little things I am forgetting. I only drove it for a year outside of the CPO/extended maintenance combo. Within that time, I changed the fluids on my own a few times according to old school maintenance.
Before I get stranded like I did with one E39 and *almost* did with my second, I will probably do the same aluminum radiator and electric fan mod on the 4.8is. It'll just be peace of mind.