1960s Ben according to the Toy Steam Bible, but that's not gospel -
http://www.toysteambible.org.uk/Wilesco-D5.htm?modid=1603&xid=1111
1960's would be older than I would have guessed. The blue painted base had me thinking newer. The photos in your link looked gray base to me. I just zoomed in and think I see a run in the front so it may well be a re-spray.(on my unit)
If it just makes the journey home safe, I will be happy!