When I first fitted a FMF 4.1 slip-on to my 08 WR450 I used Permatex Muffler and Tailpipe Sealer to seal the joins, including the join with the header pipe. After it kept leaking I realised I should have used exhaust selastic due to its better flexibility, which I've used on the join between the slip-on and the mid-pipe. However, after hammering and flexing and twisting, I can't seem to break the seal between the header and the mid-pipe. It's leaking, but part of it is obviously rock solid, which means I've so far been unable to use the stock muffler on rides in built-up areas. Any ideas on what would react with this stuff? I'm a bit concerned any more mechanic treatment might break something. The only ingredient I can find on the tube is Sodium Silicate.