I save them gas and oil caps also, Homies, Poulan/Craftsman, Mac's.
I had to replace the duckbill vent awhile back in my S25DA Poulan gas cap. Used a Homelite duckbill as the replacement. Them OEM Poulan Black rubber duckbills just eventually melt away and evaporate in the gas caps like the one that just sold on flea bay for $31 and that duckbill did not look healthy.