Thermostat housing!!!!.
I learnt a very expensive lesson after buying a 2005 mini cooper s 39.000miles fsh .
NEVER BUY A BMW MINI AGAIN!
Cost me £1380 in 5 1\2 months of ownership.
I had coolent weep from thermostat housing,and also the crank sensor o-ring!
Common on r52\3 and current models!
I also had oil leak that is hard to diagnose as oil covers the sump area,had new sump gasket first as this is common to go but still oil so had to have the rear main seal done(between engine & gearbox)
Never,never,buying BMW mini again.
Anyway hope you get it sorted!!