another thought; was it IN the gascolator or just rolling around on the floor and you happened to see it?
if the former, I'd look for exploded diagrams of the fuel pump and valve to see if maybe it has a spring check ball mechanism.I doubt that the valve does, but with all the varieties of fuel pumps out there it's hard to say unless you know exactly what you have.
If you just happened to see it on the floor as you took this thing apart, it could be anything. For example, some shop air hoses have little balls about that size under the snap ring in the brass quick disconnect...
Edit; I don't know anything about the RV12 in particular, which is teh reason I have no idea what fuel pump or valve it has