2003 R50 Mini Head Gasket?

[growingolddisgracefully]

Have acquired this sweet little Mini but she misbehaves: First off she used to run very hot - temp gauge up to Max - then spew water out of the overflow reservoir. First investigation showed a) fans wasn't running and b) radiator had a hole in it. So . . New radiator installed and fan resistor replaced, new fitted for good measure as well as a new thermostat and housing. Seemed to do the trick for a while until the overheating started again and the water/steam pressure blew the cap off the reservoir thus spewing water and steam out all over again. She's become a reluctant starter too but runs sweetly for the first few minutes whilst blowing enough white smoke (Steam?) out the back to welcome in several thousand Popes! Being an avid internet reader I'm fairly sure I know what the problem is but before I jump in and pulling the girl apart again, does anyone want to give me the benefit of their experiences and share their opinions as to what the likely issue is? BTW I have an OBDII reader and I'm seeing no sensor failures whatsoever.
Thoughts? Ideas? Advice?

[Elliot2000]

Sounds like head gasket- you can get a block tester fluid and kit quite cheap too confirm it if u want to be sure before strip down

[E-bmw]

Certainly sounds like HGF, if I saw those symptoms I would have no hesitation in stripping the top end.

A gas sniff test of the expansion tank will 100% confirm if you need it.