OKI MC562W colour multifunction laser printer/scanner/fax (Tetbury GL8)

All is working (currently using it) but the colour printing has become washed out. I've had it for over 5 years and currently it has non-OKI print cartridges so that may be the problem - or it may need an internal clean. Automatic duplex paper handling for printing and scanning. I've used it until up to today when a new smaller simpler printer arrived so I don't need it any more. Recently used for scanning old colour photos at 600 dpi as well. Includes fax.