
Forgot to mention this...
Twice, over recent months, the hydraulic reservoir has been syringe-emptied to refill it - first with Hydraurincage, then later with regular LHM.
Both times, although the pump had not been emptied (or engine started), on restarting the pump just wouldn't shift fluid, so presumably air-locked.
Found a quick remedy the second time: with engine running, operated the steering from lock to lock a couple of times, and up the pressure came up quite quickly. The steering places a very large demand on fluid flow, seemingly enough to get fluid moving through the pump. This worked on both occasions.