Budge, intrigued now: later steel pressure regulator... are you talking about the accumulator or else? If so, didn’t realise there is an “older” version - what does the original one look like? Does anyone have a photo?
The regulator is the bit the accumulator sphere screws into. Older ones were made of aluminium and Citroen replaced them with an all steel design in the late 60s and advised swapping up to the new type if replacing. Perhaps because of stress fractures? The way to tell them apart is that the old aluminium ones have a chunky screw-on cap at the top end. I can see that yours doesn't have that.
The instructions for servicing it found in manual 814 is for the old type(!) you have to source volume 3 of French manual 583 for instructions on the new type. You would need to be able to read French, but i've saved you the bother: https://ds-restoration.blogspot.com/2018/02/pressure-regulator-strip-and-rebuild.html