Is it possible to get past the valve on the fuel iunput to pour in an additive (such as Redex) on a 2017 Tipo 1.6 diesel? The flap has a strong spring - it is hard enough getting a fuel pump nozzle in.

Personally I wouldn’t bother. Save your money.

You should have a small funnel in the boot toolkit it enable you to fill the car up from a jerrycan