"the root issue is a lack of wood in the head of the stock"

Amen, and I am of the opinion that is where the cracks start, then extend and eventually become apparent at the apex of the lock. Please check the first 7 images here
http://www.picturetrail.com/sfx/album/view/17090409

and compare the wood area with these boxlock and sidelock stocks
http://www.picturetrail.com/sfx/album/view/15127852