The J-hook for my GoPro snapped a leg off, and instead of waiting for weeks for a replacement to get shipped from a faraway land, I decided to repair the one I had.
We have the technology, we can rebuild him!
After drawing up a replacement part, I printed it out on the Ultimaker, and assembled it.
The repair turned out great, the clip fits very nicely, and quite snugly into its counterpart, so I can continue to use my camera. It even fixed the slight rattle the old clip had.
[2018 update:] the other half of the clip broke and I decided to replace the whole clip.