Facts:
Head gasket done 6000 miles ago with recommended uprated parts.
Car has been overheating for the past fortnight and 'bubbling' in the heater at start up.
Established that radiator wasn't getting warm but engine was (very).
Replaced thermostat - what a pig of a job that was due to its location.
Car seemed ok for a couple of days.
Now losing coolant from the rear end of the engine but only occasionally (!?!). Have checked all pipes etc in that location and all seem ok. Appears that leakage is possibly coming from head gasket . . . but haven't positively identified that yet.
So, if the head gasket has gone again it's pretty obvious that the uprated parts haven't done their job so the conclusion is that there is is not a definitive cure for this particular K series problem.
So is now the time (after 15 years of consecutive Rover ownership) to cut my losses and change my brand allegiance?
Personally, I think it is the only sensible thing to do.