Updating this with our methodology for any future readers -- Flemster, looks like you broke off both the top and bottom nuts? In this case the top one was fine. So we took some inspiration from yours but didn't form a U bracket.

There's a flimsy metal plate covering the area needed to access the bolt. We cut that off and kept each piece we removed. Originally I had purchased the OEM stud from the dealer to reinstall; we were hoping to either find a new nut or reuse the old one. No such luck-- could not for the life of us find a nut that matched the pitch and diameter and the old one was siezed up.

Plan B was Flemster's route: we grabbed a grade 8 bolt, nut and lock washer from the hardware store. Cut the stud out and replaced it with the new one. We then welded the nut onto the frame, then welded the plate back in to place. Once it cooled down I hit it with a rattle can and torqued everything back to spec.

Definitely not an EASY fix, but pretty simple. I'm grateful my best friend is a welder with 18 years of experience. Made the job a piece of cake, and pretty cheap (bought her lunch).

Hopefully this can be a helpful guide for someone else down the line!

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