My Canon Pixma iP5000 off sets to the left?

I have been using this iP5000 for 2+ years, with excellent results, however it has always off-set the type or image about 5mm to the left side.
I'm unable to find anywhere within the "Utility" menu, that allows me to alter the positioning of the printer heads, even though "Custom Settings" (one of the options in the drop-down menu, that appears under "maintenance") gives an option to "Align heads manually".
The image is fine - just offset to the left, so text will "fall off the edge" of the sheet.
Any help most welcome.