MBP (A1398) will not boot due to not being able to mount internal SSD. Disk utility indicates it is an issue with the EFI partition. Booting from an external drive, here’s what I’ve tried so far:

diskutil repairDisk /dev/disk0

** /dev/rdisk0s1
Invalid BS_jmpBoot in boot block: c0fb8b
File system check exit code is 8
Updating boot support partitions for the volume as required
Creating a new EFI system partition
Problems were encountered during repair of the partition map
Error: -69764: Couldn't repair the partition map because a new EFI system 
partition couldn't be created


Unable to enter single-user mode on machine


No valid block 1 on /dev/disk0


sudo gpt -r show /dev/disk0
      start       size  index  contents
          0          1         PMBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6         
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640  976695384      2  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
  977105024          3         
  977105027         32         Sec GPT table
  977105059          1         Sec GPT header

From my research it seems like GUID partition is incorrect, but not entirely sure best method to resolve. Any suggestions?

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