So after going back to the garage, swapping out the fan from the old unit resolved the error messages. Everything is back to normal. From autodoc the light unit cost just over £1200. Fitting and coding plus air, oil, pollen filters and oil change cost around £700 at a local specialist. So over £1k cheaper than main dealer. In the end I didn't want to risk buying used and at least have warranty on the new unit.
Hope this helps someone.