Ok dismantled my Bird after the crash. Now i'm 100% sure it was the servo wheels slipping on the splines.
When levelling the swash today i found that one aileron servo was at its extreme limit instead of centred. So i tried to turn the servo wheel and it slipped. The screw was still in tight, nothing was loose.
This is why in the first crash it carried on in a direction i wasn't telling it to, and just before the second crash, when i had recovered from the piro and centred the sticks, it then flipped on its back and drilled into the ground.
So why after 1.5 years of no issues would this have happened?
My conclusion is, having upgraded to 8S, I wasn't accustomed to the response time of the heli during manoeuvres. My efforts to correct the heli where extreme. The fact that i had upped the servo voltage from 4.8 to 6V was putting more than the usual pressure on the wheels, causing them to slip under extreme load.
I have now installed the metal Align servo wheel. I am super impressed with the strength of the Chaos 600. I absolutely love this bird and it hurt me to see it go in for the first time in 1.5 years of awesome flying.
But it will be receiving some love and attention, and a new look that you'll have to wait and see.
All the best
Lee