Many thanks to all for the help.
I've pinned the leak down and its from the anti kickback port of the box at the bottom of the steering column! The pipe has a minute crack so I'm getting one made and changing the underlying o ring at the same time. Preferable to splitting and splicing , I think!
BTW as a uk owner I sometimes buy through my American brother in law at savings that can be 90% ! A starter motor over here would be about $1500 and yesterday I paid $25 for 10 of the small o rings that sit on/in the diesel filter. I assumed from the price that they must be something special but they certainly don't look like it! Hey ho.