How (not) to sell a van

I am currently part owner of an ex-Royal Mail van -- it feels rather like owning part of a race horse. To be precise I fronted up some cash for the son to buy HIS share in the said van a couple of months ago, to go round Europe on a tour with his band (that is, George Wright and the Keynote Speakers, if you fancy a listen).

Anyway, now they are back, they want to sell the thing (a proud red beast, as you see in the pictures, which toured the extremities of Europe without the need for...