fuel nozzle overflow cap missing.

[blitzen Bspec]

Hi people, On my blitzen wagon the flat round metal spring cap on the entrance to the fuel nozzle is missing and has since having the car. so when i start the car the fuel tank smell comes out and stinks abit. should I try and find another nozzle with the metal flap. I guess this would prevent contaminants getting into the tank. I still have the plastic filler cap which covers the filler hole