1320c Printing Faint Colours

I've had a trawl through the archives and not found a resolution to this yet.

When printing text with coloured sections, the colours appear faint and washed out.

I've changed the cartridges (which weren't empty) with no effect.

The fuser has had all it's transport clips removed (that I gather could be a cause).

I've been into Printer Status and all appears OK.  (Control Panel > Printers > select 1320c > Adjust Print Options > Printer status (at bottom).

This happened suddenly, and hasn't been a gradual fading, and no settings have been changed or driver upgrades etc.

I had the faint blacks, with black appearing as grey, about a year ago, and that was an electronic setting (tried several resets and power cycles and it immediately came back to normal), so wondering whether this is a similar memory corruption? However have tried a couple of resets and power reboots with no effect.

Any help please?