Looks like the head gasket has gone on my 2007 i6. Not 100% sure as it still pulls like a train. However the coolant does pressurise but not hugely but definitely more than normal. Oil smells a little burnt too. So where is the best place to get this checked for sure and then repaired. Where is the best ace to get the head gasket set from?

Some history might be relevant. Couple of years ago the engine oil cooler ruptured. Garage change every coolant hose thermostat radiator water pump etc. Car ran ok. I have had intermittent issues with coil packs but all have now been replaced. Thermostat was changed about a year ago again. Now it’s got colder it has only now become apparent that the heater is blowing cold. Used Holts radiator flush and it did help for a few days but not getting really hot like it used too. A year ago it was treated with head gasket repair liquid an expensive one with great reviews etc. I just want my car to run normally