This is a typical spot for boom tube damage, unfortunately impossible to repair with any margin of reliability. The whole motor boom assembly must be replaced, and this is not easy task. Booms can be found on eBay, Left or Right when looking at the bird from front. Two kinds of booms can be found: early model with metal bushings, later replaced with lubricated rubber (see photo). Carbon fibre tube pattern is irrelevant, bot types are compatible. The nut adjusts boom play along axis. Good luck with repair ...