Disco 3 heater fault

I have a Disco 3 (55 plate) and the heater has gone faulty. It blows hot air one side of the car and freezing cold on the other side even though both temperature controls are both set on max. I spoke with the main dealers who said it either needed a "download" or a "blend motor", the latter requiring the dash out which would be a major job. I don't want to spend a fortune at dealer rates without doing some homework. Has anyone got any ideas/experience of this?

Get a second opinion from a local independent, somone with an Omitec UCM or Autologic.