My wife has a 2008 Cooper, not an S, 42k miles, full service history, it has the tensioner / timing chain problem, I live in Ireland, we have had several Mini Coopers, this is the last one, our local dealer wanted €380 to assess the problem with a total estimate of between €1100 - €1800 to replace, this total cost and parts may or may not have a goodwill contribution, to be determined AFTER I spend €380 with the dealer...yeah like I am an idiot !.
I had the tensioner and chain replaced with an Indi costing €700 last week, it is back in the independent garage today with more chain rattles....additional part required, cost yet to be provided, estimated at several hundred....so total cost to me of replacing the timing chain, tensioner and whatever they are at in the garage now is probably over €1000, this is by far the largest repair bill I have had in over 30 years of driving, to boot for a part that is not even a service item, the chain should last the life of the engine, I have a 1970's car in my garage that still has the original chain !
This is a problem that is well known, google Mini timing chain USA, you will see after threat of legal action Mini USA stepped up.
I would not recommend buying a Mini, even if this work is done it does not guarantee no failure at some later point.
The reality is that this fault was in the car from day one, Mini care less, Mini adventure...?, rather a MINI disaster..., buy a Korean car with a 7 year warranty....Mitsubishi do an 8 year warranty....