I neglected to add that, when Bert and I were diagnosing the problem, I took the opportunity of checking the thickness of the old O rings compared to the new.

They were 1.5mm thick, whereas the new ones are a tad under 1.8mm thick, so there is some validity, I suppose, in replacing just the O rings first, as they appear to be the sole sealing point between the EHA and the fuel distributor orifices.

Looks like the life on the old O rings and EHA was 100k miles.