+1 Bought mine with 90k, minor wearNtear fixes but it's all good.
Plus I don't mind working on these vehicles.

Like any car, I would continue to own my X5 once it has 120,000 miles on it; however, I wouldn't buy someone else's 120,000 mile car.

I would try to stay below 70,000 miles.

how much are they asking for it?
it should be almost free with that mileage.

Everytime i take mine to my service man he always makes a comment on how well built these x5's are compaired to the ML's including the new ML's.

If you have access to the service history that will tell you everything you need to know and some! If it has been maintained then don't worry about it as much! Parts will need to be replaced eventually thats a given. You will be able to tell how well the X has been maintained when you see it and drive it! Trust your gut despite the price. Good luck on what way you decide to go!

Even if you work on your car yourself a potential transmission failure would be a no go for me at that mileage.