BTW, I have visited the official OS site - no picture of current models there seems directly relevant.

The strings are held in by slots in what seems a bar of aluminium, they appear to 'ball end' types - but not sure what set "A, B, C" types are meant to be the replacement.

The missing string is the wound D in the low (incomplete) octave - the D above the C two octave below Middle C, by looking at the 'keyboard indicator'.

Not prepared to try buying just one yet, because I have to get my tuning gadget from home... who knows how many more may die?

Still missing a couple of low strings from my Roseharp set...