Greetings Marvo, quotes:
"I only remember one accumulator on each side?"
I couldn't remember either, so I looked at my first FCOM, dated 17 Feb 1988 (!), for the BCAL-ordered 100-series (G-BUSB/C/D/E/F). It clearly states the LAF operates Spoilers 4 (Yellow hydraulics) and 5 (Green), as well as Ailerons (Green & Blue). So there must have been two, surely? Maybe only one was visible when we extended the Flaps... Could it have been the other one that needed topping up?
"we used to top them up with nitrogen each turn at LHR on the old -100 series (ex BCal) BA G-BUS aircraft."
Rubbish! You engineers never cease moaning.
BTW, the BCAL-ordered 200s (G-BUSG/H/I/J/K) definitely had the same system, but perhaps the accumulators were less leaky? Can't remember if the much later, BA-ordered, A319s had it.