papa_sierra,
Definitely a fatigue failure due to, what is in my opinion, poor design. Here's a picture of the mixture cable in the ICO position:
The mixture control wire goes through a hole in the vertical pin which passes through the aluminum washer and then through the gold coloured mixture arm. The castellated nut at the bottom pulls the pin and therefore the wire down onto the washer. In order to fix the wire without clamping the assembly to the mixture arm, the washer has a concave top, so that the wire is bent as it passes over the edge of the washer and then bent again as it goes through the hole in the pin. Significant potential for fatigue failure at the contact points.