Hi number 6 is rubber grommet to prevent water not going down injector it don’t stop any gases and unfortunately they don’t stop water early Ducatos famous for scuttle panels leaking water over everything fiat used cone injectors up to 2014 we have loads trouble sealing them after roadtest if you spray fluid over injector you’ll see gas bubbles Iv known reaming tool to make seal worse check end of injector if really rusty big trouble use new clamp ,,bolt and washer and lot of luck don’t want to curse your job I feel your pain good luck