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I don't think that I'd try a repair until the I understood the cause of failure and even then I'm not sure I'd trust a repair done at a point that failed. The big problem that I see is that you can't stagger the scarfs of the wood strips, so now you'd have a two scarf joints at the failure point.
Yeah, that bothers me too. I'm trying to figure out how to cut back the mast wall skin to allow me to get deeper into the mast sections to stagger the scarfs, particularly the leading and trailing edges.

In the first picture, is the dark line running from the leading to trailing edge a couple inches below the end of the web a scarf joint? Also, in picture 3, it looks like there is another dark line running from leading to trailing edge on the upper side just below the break.
You're right. Both of those dark lines are scarf joints in the ply sidewall material. One is 2" below the break, the other is within a 1/2" of the break. The solid wood at the leading and trailing edges have no scarfs within sight. The web, and it's solid wood gussets appear to be broken, but it's not completely clear that there was not a joint there (see note elsewhere about a staple runnung across the grain of the plywood web). The outside of the gussets has a carbon tape running vertically the entire length of the mast, and Malcom said the tricky part of assembling the mast was properly locating the web as the 2 halves were laid together. It's possible that there was an insufficient amount of thickened epoxy between the web and the mast sidewalls in this (and other?) areas. They are separated in this vicinity now, hard to tell if it was prior to the break, or as a result of the break.

"...the forces were transmitted up the mast to the first weakest point."

It doesn't work that way. The vast majority of the boom compressive force is taken up by the mast step. If the force from the boom is 100lbs, the mast is 36ft long and the gooseneck is 1ft above the step, then 97lbs of the load is transmitted to the mast step.

Gooseneck is 18" above the mast step, and the builder said he replaced the original mast step (delrin ball on 1.5" s.s. post) with a stouter version, as a result of the first one bending. That, coupled with my observation of the substantial amount of boom flex, makes me real aware of the amount of force the boom is applying here.
I agree wholeheartedly to the importance of understanding the reason for failure before investing in a repair. I really appreciate all the insight, questions and opinions being offered here. I'm happy to send higher quality pics directly to anyone wishing to help me explore this further. It's a gorgeous mast that I'd love to salvage if it seems feasible and justified.

dave