I am in the process of shopping for a R53. I have done some research and am aware of the usual R53 items to look for. I drove this one today:
2005 MINI Cooper S minicooper only 50K 2 Door Hatchback
It has a check engine light on, and the drivers window makes a snapping sound when it is near it's closed position. (I am pretty sure I can fix the window) The car is bone stock. I looked in the usual places for oil leaks and without putting the car on a lift, I didn't detect any leaks. Even the coolant tank looked original. I saw the carafax and it is indeed a one owner car. I'll be taking it to a local Mini specialty shop unless you guys can point out any red flags. Any input is appreciated ahead of time.
Thanks,
Steve

 

I would check the clutch and see how hard it is to engage. that can be a costly fix(a clutch cable replacement can be a ten hour job.) usually it involves a differential replacement or repair as well. The problem is these cars were made to be manufactured not repaired. Like the original Mini they crammed an awful lot of motor into a very small space.

As for the oil leak, what I would do is take a sheet of 4' x 3' white paper and put it under the motor/transmission, around six hours later and take a look.

Good luck

 

Always a good reference point: MINI R50/R53 Buyers Guide - MotoringFile

Even with that mileage, I think they're asking too much. KBB, even at excellent condition, puts it at $6,700. I'd compare it with truecar.com and other MINI's that are similar on craigs list. It looks like it'll need new tires as well. I'd ask them to replace them if you decide to purchase it. The check engine light is concerning. I'd pull the code and find out why it's on.