Retainer 18569 used with Tank O-ring 18303-01 on Fleck 7000 Valve,
also used on the Fleck 5800 Valve ( but not 5810,5812 )
Also is part of the old Fleck 5000 valve body, and cross references with Rainsoft PN 19328
This retainer ring "locks" into place
and is extremely difficult,
if not impossible,
to remove without breaking it.
So, you are only going to "replace" if your current ring is clearly broken.