The steering gear boxes on the Argosies (and Classics) have steel piping to the gearbox connections, no hoses. Typically the only hoses in the power steering system go from the PS pump to the hydroboost, one pressure and two return.
The steering gearbox will have two seals, one for the input shaft from the steering column and the other for the output shaft. My guess is the output shaft is probably leaking if the leak is at the gearbox itself.
Here's the
gearbox I bought to replace the gearbox on my 74 Argosy. According to Rockauto the 74 and 77 have the same gearbox.
When I replaced mine I removed it and took to the local autoparts store and they ordered a replacement. Since you're in the UK you might want to do some research to ensure you get the right one.
While replacing the gearbox be sure and replace the
gearbox coupler. The thing to watch for when replacing the coupling is to make sure to match the spline count.
Be prepared to invent some new cuss words because getting access to the bolts holding the gearbox to the frame is almost impossible. Also be prepared to dismantle parts of the front grille to gain limited access.
Brad