cannot unlock bootloader, cache partition probably corrupted

Hello all,

My Nexus 7 (2013) was bricked about a year ago by a google update, like many other. I just got around looking into it now. I'm having some trouble as you may have guessed.

Here's the current state of affairs :

• Cannot get past the white Google logo


• Can boot into fastboot


• fastboot is locked


• bootloader version is FLO-04.02


• Can boot into recovery mode


• factory reset fails on mounting /cache

Here's what I've tried so far, from several sources here and there

• Download Official Android image and run a flash-all.sh


• unlock the bootloader with `fastboot oem unlock`


• factory reset from recovery mode

All of these end up failing because bootloader is locked or because it freezes (most often at some kind of wiping data step).

This is the output of the `.flash-all.sh` command.

Code:

---

floby $ ./flash-all.sh
sending 'bootloader' (3911 KB)...
FAILED (remote: Bootloader is locked.)
finished. total time: 0.005s
rebooting into bootloader...
OKAY [  0.006s]
finished. total time: 0.006s
archive does not contain 'boot.sig'
archive does not contain 'recovery.sig'
archive does not contain 'system.sig'
--------------------------------------------
Bootloader Version...: FLO-04.02
Baseband Version.....: none
Serial Number........: 07cd6455
--------------------------------------------
checking product...
OKAY [  0.003s]
checking version-bootloader...
FAILED

Device version-bootloader is 'FLO-04.02'.
Update requires 'FLO-04.05'.

finished. total time: 0.019s

---

I cannot post links but here is what it looks like:
image svRKQ5g on imgur
image y5Pa3br on imgur

Do you have any idea how I can unbrick this ?

Thank you all in advance.