ChristiaanJ,
The best photo of the ribs containing the wing brackets or wing rib feet is depicted in machaca's post #78 on page #3, first photo. The multiple rectangular things that stick upward out of each rib, each with four holes, are the feet. I assume the type 1 cracks come out of one or more of these holes in certain locations. The shape that connects these to the actual rib is where I think the more serious type 2 cracks developed. I guess the cracks are more random in nature that what I would have thought.