I have two Evo 1.00nx's and both had the problem .. I fixed mine with a small sheet metal screw ... just drill a small hole where the half's meet ...make sure that you tighten the muffler well before you do or you will see a lot of black rub oil.

I have also seen this happen on the Evo .46 as well.

Here is a handy tool that I use that will install to you web browser and check your spelling

http://iespell.com