I've found several posts which state that BMW's official line is that there's nothing wrong with the car unless it consumes more than one liter for every 1,000 miles. Your son's car is beyond that
Since you reported the problem before the warranty expired, the fix should still be covered.
There are lots of scary stories out there regarding R56 MCS
oil consumption and engine "coking". Do some Googling if you already haven't done so.