Head Gasket ??

Ok a question to all the mini guru's .... Temp gauge constant ( sits happily in the middle ) ... heater still blowing normal ( warm and cold ) ... Mech at garage says my oil leak looks like mixture of coolant and a little oil .. when engine turned off, header tank coolant becomes very low, on start it returns to normal .... Mech says Head Gasket or perhaps worse .... I'm not so sure .... any thought are are very welcome ...

The temp gauge is a waste of time so ignore that...

I'd tend to go with the mechanic, pending relevant tests - mayo under oil cap? Compression test, pressure test etc

Get a sniff test done on the coolant /expansion tank