The front end popped off with the right leverage as did the new replacement pop back on.
However, unlike the two previous times, the rear ball wasn't aligned close enough to pop the rear end on as I couldn't lower the front suspension (or in this case, raise the front wheels).
What I did discover was that the corrector arm could be levered backwards enough to line the joint up (if only I knew this before!!) - and it became apparent just how worn the old arm was as it required far more pressure to pop the new on!
Both felt washers were present and seemed in good condition but I can't work out what their purpose is as they just seem to sit behind the ball doing nothing.
Once again, thanks to this forum and the kindness of human nature that make it possible