MGS rear header pipe. The bend in the rear is so tight that the pipe is not 100% round, this causes the spring clip in the exhaust flange to not stay in the flange seat. Fix- Move the clip up to the end of the header pipe, and move up the flange to the exhaust port studs, and tighten up the flange will pull the header pipe to the gasket and seal. Check and tighten with 1/4" drive 20-50-100 miles when engine is at temp.