I agree that you should not wash the engine on these cars.
I disagree that this car can't be rolled back. Digital meters are much easier to roll back then old fashioned ones. Trust me, I can get any car rolled back for about 150-200 UK pounds. I have seen RS4, M5, Range Rovers etc etc getting rolled back and it is simple. Just plug in and play 
@All
If you want to know the EXACT mileage of this car. Just take the car key to a BMW dealership and ORIGINAL mileage is recorded on the car key for BMW. That's how I always get my BMWs checked. I took my key to BMW dealership last week to get it checked and they told me everything. Said that the car got 83,000 miles, service due in 13,000 etc etc and I asked how do you know all that, they told me that the BMW ECU keeps mileage back up and other information onto the key/s so if anyone tempers with the mileage, the key never lies 