R56 Cooper N16 engine coolant loss.

Hi
My wife has an 80K miles 2012 R56 Cooper (N16 engine) Recently it has started to loose coolant and I cant find a leak anywhere. I replaced the thermostat and the stupid pipe about 10 months ago and cannot see any leaks from either of them. There is no noticeable oil in the water or water in the oil, and it runs fine. Connected up an OBD temp gauge and the temperature is running about where I expect it - I know r56's run quite hot - it ranges about 205-215F so 95-102C. Are there any other places these engines loose water from - are head gaskets an issue on the non-turbo cars?

thanks for any pointers where to look next.

check the radiator expansion tank
the are prone sometimes to crack

Another for checking the expansion tank