Mix equal amounts of Linseed Oil (boiled or raw does not matter) and Turpentine (white spirit will do) add a dash of Methylated spirits if you wish(not essential).
Wearing Latex or rubber gloves is essential.
Apply with a soft cloth using gentle circular movements, as you would with metal polish or furniture wax.
This is absorbed into the built up layer of wax and dirt and softens it,then starts to remove it with subsequent applications,in the process It will "blend in" any recent scratches without harming the original finish.It stinks a bit though,but that passes.
Ferg
April 2010