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You're going to want to remove as much adhesive from the parts (both the original, and what the applied), and then re-glue with a much more substantial adhesive. There are specific ones you can buy for CF-to-metal, but JB Weld epoxy (get the slow-drying, not the 5-minute version) is easy to find at most home improvement warehouses, and it will work fine. I'd advise some masking tape be applied to the leg and spider in areas you don't want marred by excess glue, and you can pull the tape off after the glue has fully dried.
FWIW, I don't believe this failure is as common as you may have been lead to believe, but obviously, it happens. If you've got your purchase receipt from an authorized US dealer, Gitzo will repair it for free.