Ah!!!... Theres the rub (so to speak) lol

This file should be owned by root (UID=0)
So.... as root do this:

Code:
chown root:root /etc/sudoers
Also the file permissions may need to be reset with something like:
(as root)
Code:
chmod 0650 /etc/sudoers
Im curious to know how this file came to be owned by UID=1000 (which is you BTW).. did this file get deleted somehow causing you to have to re-create it? Any guess?

Hope this helps,
-Justin
One Mynds Eye