Use the GB27 Odin one click stock root to ensure the device is updated and working properly. Luckily for you, download mode isnt affected by a bad kernel flash. The one click will put the GB27 Kernel and modem and upgrade it to 4.1.2.
Then if he wants 4.0.4 back you can always downgrade with a 4.0.4 Odin one click.
But before you do, use the triangle away apk on the rooted GB27 after odin to take away that yellow eyesore .