Business laser multi function printer (Walnut Tree MK7)

This is a HP multifunction printer with scanner and duplex ability. It is working but has something not quite right about the distribution of the magenta toner so that the colours on the left of the page are not the same as on the right. Not really a problem for general home or office use but not acceptable for my printing business. Please be aware that a full set of toner for it costs a couple of hundred pounds. Currently there is toner in it, although the cyan is low.