Hello. I have just bought a complete exhaust system for my 2004 Navarra. 2.5 D22YD-2.5TD Crew cab. There is a crush ring in the fitting kit besides 2 gaskets. Can someone tell me where the crush ring goes please ? Is it between the back box and the middle box and if so do you also use a gasket there as well ? Thanks in advance for any help, guidance etc.