Has to be the purchase experience. Starting with a "warm up" 4.4 that is now being rather fastidiously cared for by Happy and his daughter.
It was a great intro to the Xoutpost community and really wetted my whistle for the chassis/motor and, like a gateway drug, wanting to experience the first "M" X5.
But that purchase was the one and only time I've ever bought a vehicle sight unseen, 1700 miles from home... and trusted a car salesman (at a Buick dealership!) regarding condition of a vehicle. It turned out okay, but yeah, it was a "puckering" decision/experience. As EODguy is frequently pointing out, I don't know how I'm still married... or had some "accident" occur resulting in my leaving this world behind.
For anyone interested... a full story/writeup about the purchase trip is
linked here. Fair warning, it's long. I was excited, and 9 years younger than I am now. Cut me some slack.
I've only put about 40k miles on the truck in those 9 years, most in the first 2. Shortly after purchase we put about 3k miles on it taking my daughter and MiL all over FL to visit family. We've had good times in the vehicle for sure and both kids are already fighting about who gets it when the time comes. My wife always jumps in for me... lol, "sorry kids, Dad's getting buried in Red."
And, as all E53 owners know, especially those brave enough (read dumb enough) to be equipped with a V8 variant: the sword of Damocles is always present. Red's VSS are getting worse and who knows when the mickey mouse gasket will let go... but I'll be damned if I don't love this truck and smile every time I fire it up.