I agree and understand how the vacuum secondaries operate. The bottom side of the pot is atmospheric (open to air), so you're correct the fuel has to get through the diaphragm to come out at the shaft. This is why questioned it being fuel and possibly water condensation instead, until I saw the plastic cover over the carb horn sealing off the carb from venting any gas trapping it in the manifold system. This is the only way I can see the fuel entering the vacuum port leading to pot, once the diaphragm deteriorates allowing the fuel to vent, even more fuel will be pushed in due to the lower atmospheric pressure.
All do respect, I too am only trying to help.