After applying the Colour Fading Fix (cleaning the dust from the optical box), the colours were fine but were just a little out of alignment. I forced a calibration from the Main Menu and things seemed to improve, but were not quite right. I repeated the calibration process a couple of times, and it got worse.
I created a test page with vertical and horizontal line segments in the colours of the cartridges. Vertical segments near the right hand edge are reasonably aligned but it gets worse towards the left hand edge where the cyan and black are as over 6mm apart. Horizontal segments are consistent with a maximum variation between black and magenta of about 0.5mm.
It seems that every time a calibration is performed, either automatically or manually, the alignment gets worse.
Any ideas?