Yes, I have taken one apart. I am pretty sure you can't fix it that way
for several reasons, one of which being the wires inside are too short.
It does not "willingly" come apart. And I would guess that the ring in there
is pretty hard to find. Seems to be a square cross section.

I'd suggest you put the pump in a jug of clean gasoline for a few days,
take it out and hook it up with hoses and a bypass pressure regulator and
see how it does. You might be surprised (assuming it pumps well now).

You can run the same fuel line with either the electric pump in back
or the mechanical in front. Just gotta fabricate a sized adaptor to
put in place of the electric pump in the hoses. All the B18/B20/B30s
use the same pump and have the same eccentric on the cam.
--
George Downs Bartlesville, Heart of the USA!