My Nexus 5 just failed yesterday. In recovery mode I get this message:

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1. Supported API: 3
2. E: Failed to mount /cache (Invalid argument)

I followed this tutorial step by step by whenever I try to "flashboot flash" something (cache, system, etc.) I get this error message:

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1. FAILED (remote: flash write failure)

I can confirm the bootloader is unlocked:

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1. fastboot oem unlock
2. >> unlocked: yes
3. >> finished. total time: -0.000s

More details:

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1. fastboot getvar all
2. (bootloader) max-download-size:         0x40000000
3. (bootloader) version-hardware: rev_11
4. (bootloader) version-baseband: M8974A-2.0.50.2.30
5. (bootloader) version-bootloader: HHZ20h
6. (bootloader) version-cdma: N/A
7. (bootloader) variant: hammerhead D821(H) 16GB
8. (bootloader) serialno: (not displayed in the forum)
9. (bootloader) carrier: None
10. (bootloader) secure-boot: yes
11. (bootloader) unlocked: yes
12. (bootloader) product: hammerhead
13. (bootloader) partition-size:aboot: 80000
14. (bootloader) partition-type:aboot: emmc
15. (bootloader) partition-size:boot: 1600000
16. (bootloader) partition-type:boot: emmc
17. (bootloader) partition-size:recovery: 1600000
18. (bootloader) partition-type:recovery: emmc
19. (bootloader) partition-size:system: 40000000
20. (bootloader) partition-type:system: ext4
21. (bootloader) partition-size:userdata: 3321fa800
22. (bootloader) partition-type:userdata: ext4
23. (bootloader) partition-size:cache: 2bc00000
24. (bootloader) partition-type:cache: ext4
25. (bootloader) partition-size:persist: 1000000
26. (bootloader) partition-type:persist: ext4
27. all:
28. finished. total time: 0.037s

Following this thread I suspected a problem of size so tried to increase max size:

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1. fastboot -S 2048M flash system system.img
2. erasing 'system'...
3. OKAY [  0.126s]
4. sending 'system' (1020657 KB)...
5. OKAY [ 32.239s]
6. writing 'system'...
7. FAILED (remote: flash write failure)
8. finished. total time: 32.537s

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1. fastboot -S 2048M flash cache cache.img
2. erasing 'cache'...
3. FAILED (remote: failed to erase partition)
4. finished. total time: 0.217s

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1. fastboot -S 2048M flash recovery recovery.img
2. sending 'recovery' (10014 KB)...
3. OKAY [  0.521s]
4. writing 'recovery'...
5. FAILED (remote: flash write failure)
6. finished. total time: 0.708s

I am now clueless... This is a 5 year-old phone so it could possibly be a hardware failure but I really really want to make sure I tried everything I could to save the guy!! (even though data is long dead by now).
Any thoughts?