Retainer for 1.05" distributor orings 5600, 6600, 6700, 5000, 5800, and 2510
Rainsoft Cross reference - PN 18445
For some reason this part is not shown in most of the Fleck Diagrams.
It is simply "pressed" into the center opening for the distributor.
The o-ring ( 13304 ) sits just immediately above the retainer.
The retainer is what keeps the o-ring in place.
So, you just need to take the retainer, and force it into the center opening of the valve body at the bottom.