Up with the lark, mucked out the pigs, and it still wasn't raining (quite a change from recently) so with no delay I got 'out and under'
Whipped the cover plate off, undid all four pipes (as the servo ones are to the rear of the main drive one), swapped over the servo pipes, replaced the main drive ones all with a minimal oil loss, as this time I knew that a Sharpie pen with a rubber glove over it neatly plugged the pipes

Cleared the deck of tools and drip trays, up into the cab, lifted her up onto the dozer blade and dipper arm so that the track were off the ground, and gave it a try ....
IT WORKS
WE HAVE TWO SPEED TRACKING

Rather a relief actually, as if it hadn't been that the chap had inadvertantly reversed the hoses at the Orbiter, then I really would have been stumped for the next move