R400D - Possible head gasket issue?

[Tomiam]

Finally got time to get this sorted.
Undid a bunch of pipes to release the old coolant and then stuck a hose pipe on them to flush them through.  Much to my surprise there was no 'mud' in the pipes or radiator.  Only at the top of the expansion tank as a very thin film.
Got it all running clear and then let it drain for half an hour whilst I went to Halfords and got some G30 coolant.
Installed the bleed piece I mentioned earlier up by the heater as well.
Filled her up, bled out the air through the top of the radiator & t piece.  All went well.
Left her idling for 15 mins or so with the cap off to assist with air removal. 
Took her out for a test drive for 20 mins and temp never went above 80 on the gauge.   
Left her in the garage overnight and there are no pools of coolant on the floor this morning. :)

There is still a hesitation in the engine at just under 2,500 rpm but that's got to be something else and not connected to this.  Im just relieved its not a head gasket failure as Im sprinting this coming weekend!

Fingers crossed this is now solved! Thank you all very much for the advice and steerage.

Next step, to teach myself about about throttle body balancing and throttle position sensor settings. :)
 

[JNC]

Another tip when the car is stone cold ie before first start of the day undo the cap on the  T bleed there should be no pressure and top up through T piece with coolant  it won't be a lot  but the more air removed the better ,  hold the T as high as possible . Do not remove expansion tank cap. Air will always settle at the highest point  that's why hold the T high as possible .