Hi Brownieseeker,
That's a lot of broken leaders.
I have fished Avington quite a bit and landed many doubles, but never felt the need to go above 9lb Riverge fluorocarbon. I can't remember the last time a fish broke my leader.
Are you sure your knots are being tied properly? I have found some leader brands knot better than others, with the knots I use anyway, and Riverge has always performed well in this respect for me, even with an explosive double at short range.
A simple tucked 5 turn half-blood knot at the fly and a 4 turn water knot at the other end joining the leader to a permanent short piece of 18lb mono that's nail knotted to the fly line. This set up works for me.