i had similar issue some time ago.
in my case there was some offsetting between the colors but in black it was perfect.
i installed the drum drive update kit and it was not the reason.
the right cover was a little slippy and need some tighten only.
the justification was that the charge roller of the transfer belt is in poor contact so that the image is almost reproduced every 13.Cm.
try to push the right cover inside and monitor.
good luck.