X5M with the S63 engine is a blast to drive. But the engine isn't the most DIY friendly, as analyzed by Nathan here:
https://www.youtube.com/watch?v=n75gMnrYBcE
N63 and S63 are virtually the same design.
I own one and it has 71,000 miles now. I am very careful with the engine maintenance, changing the oil at every 5,000 miles, using Liqui Moly 5W40 and Mobile 1 0W40 with oil saver additives.
I let it idle for a few minutes after driving so the engine and its turbo can cool down. I even took off the engine cover to allow better heat dissipation.
So far so good, but I won't buy one like yours with so many miles on it.