I hope it is not head gasket, if you could get cooling system pressure tester you might be able to pin point where leak is, but when you said it is in oil then it is usually like you already fear head gasket, our cars have no coolant running through manifold just through throttle body but then there...
I used Peak Global Lifetime Antifreeze, if you read up on it you will see that specification are matching your owners manual.That is what i used and my vehicle is 03 gt.here you can buy it at Walgreens. Check their website out http://www.peakauto.com/antifreeze-peak-global_lifetime.shtml" oncli...
Try doing this, unplug battery, let it sit for few hours if possible, so ecu can reset, also if you have code scanner you can use it to reset ecu, this will clear ecu memory, make sure heater blower is on off position then start the car.Let it idle and do not touch gas pedal. let it idle till it rea...