Just finished grinding down both sides of the foothold and laid 2 layers of 15 ounce biax on the back to make it a whole foothold again (2 pieces broke off while grinding). I'll let that set up overnight then put one layer on the inside before putting it back on and using Great Stuff to get me by this summer.
I'm not sure if I'm going to do the left foothold or not, it's not broken yet. I'll see how strong it feels before deciding.
The hold that broke doesn't even feel as thick as one layer of my 15ounce where it broke, other portions seem a little thicker but not much, however it's all just random matting, not woven cloth.
Crammit: I only put the 3M in between the flange and the hull as a waterproofing barrier, none of it makes it to the edge where the fiberglass bonds. I screw the foothold in first with the 3M, let that set up, remove the screws and glass it in for the permanent bond. This foothold just slid right out after cutting the glass, because the 3M and foam bonded to the spray paint on the back and it released from the foothold. Since there was no bond there, the inner portion could move slightly against the compression of the foam and eventually fatigued and broke.