[PaulE]

Is this different than the vent line flapper thing you replaced?

996 Owners! Check out our Fuel Fill Solution DIY! - Pelican Parts Forums

https://www.pelicanparts.com/techarticles/Porsche-996-997-Carrera/FUEL-Fuel_Filler_Adapter_Ring_Installation/FUEL-Fuel_Filler_Adapter_Ring_Installation.htm

https://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=997-201-944-00-OEM&catalog_description

My car used to have an issue where it became difficult to add more fuel after it got to about 3/4 full while refueling. But it seems to have gotten better with age so I never got around to doing this. I hope it is what you are looking for.