To decide If it is a faulty, damaged, or worn-out screen it might help to know if it has been this way since the device was new, or did it become worse over time?
Also there were some firmware versions that had ghosting issues on some devices, so it might help to know what version you are running.
But then the original Aura N514 was a bit of an oddball, it has a different screen type / screen refresh combination than any other Kobo device before or since, so even if there is nothing wrong, what is reported for other devices might not necessarily be a good guide to what you can expect on the Aura.
Edit: Since firmware 4.8.10956 there seems to be a new setting that can be added to the [Reading] section of the "Kobo eReader.conf" configuration file that might affect the screen refresh on the Aura:
Code:
[Reading]
disableRegal=true