Dell c1765nfw: can't print straight.

Hi,

I'm having an issue with my c1765nfw: when I print, the left side of the page (portrait) is printer bigger than the right side of the page. Let me try to explain better: if I print let's say a rectangle nearly full size with vertical sides of 28.6cm. When I measure the left side of my rectangle, I get 28.75cm; but the right side will measure at 28.45cm...

This is giving me many issues just as it is. But when I try to do dupex printing, it gets even worse (as the gap seems doubled when comparing one side to the other).

Is there anything I can do to correct this?

I've updated the printer to the latest firmware. I've looked at all accessible rollers and didn't find anything strange. Any help would really be appreciated!!

Thanks!