Xerox C600 colour registration issue

[TheMadHouse]

I've got a recent (few months ago) problem that's occurred with a Xerox C600, where the colours are vertically mis-aligned.

See attached image, the last green "Hello" clearly shows how far out the colour registration is.

I have tried (as per Xerox's suggestions from their website)
- Cleaning density sensors
- Cleaning LED lenses (using the supplied cleaning rod)
- Colour calibration (from the menu)
- Colour registration (from the menu)

Anyone suggest what might be wrong and what to try next?

Thanks



Jim