I found why I blew a seal...


I was originally using a Central header with a tuned pipe.... I had installed copper shims (supplied with the header) in the exhaust manifold. The shims prevented me from properly tightening the Slimline muffler.


I removed the shims, Slimline sent me new seals ( Thanks ! ), and after 11 flights so far, no signs of loosening.


Thank you,