It must be replaced every time the muffler is replaced. Otherwise there is a risk of air ingress and a risk to your cylinder.Adly (Her Chee) Air Tec 1 50Adly (Her Chee) AT 50 (City Bird)Adly (Her Chee) Cat 50Adly (Her Chee) Jet 50Adly (Her Chee) Noble 50Adly (Her Chee) Panther 50Adly (Her Chee) Pist..