In thinking of buying an x5 with about 120,000 on the clock.what mileage do the gearboxes go wrong and what else goes wrong at about 120,000

What model/engine are you considering?

I only have experience with V8 versions but here goes, History is important and when trying/testing make sure absolutely everything works as it should, every button every knob (there are no cheap fixes if there were then why hasn't it been done?)

Get the car up to temperature and give it some beans changes should be smooth both up and down the box in all modes D, S, M. When slowing to a stop there should be no jerks shudders or clunks. If there are walk away there are a lot out there. All the engines should pull strongly and be smooth and quiet, temperature should be in the middle of the gauge and not move. The gearboxes are used in many models by other manufacturers (BMW choose to say they are sealed for life) yet the box suppliers have fluid and filter change service intervals. With both X5's I have had the gearbox fluids and filters changed along with the transfer box and diff oils as a matter of course (preventative maintenance if you like) and have had no issues (touches wood)

Remember by the nature of a Forum it is mainly for people looking for answers to a problem so you will read more tales of woe.

I don't think there is any difference in reliability in BMW than any other manufacturer so at 120k providing the History is sound and the car drives well then I wouldn't be put off.

We brought ours as a cheap tow car for a horse trailer after selling our horse lorry. The first was a 4.4 that was written off by a falling tree a good car. The current one is a 4.6is even though it was low miles (68k now 94k) I still did the fluids and filters and it drives really well.

If there are issues with X5's I would say suspension bushes (made from finest butter) I have heard the argument "it's a 2.5 ton car" well they knew that when they made it so should have bushes that last more than about 50k. I have had no air suspension problems but have read of many who have, but again that is what a forum is for.

Good luck with the test

Thanks for the advice.