Header exhaust leak - help!

You need to look real close at your header in that area. I thing it's the weld on the header surface Not, the gasket that's your problem.

I had a set of Hooker comp headers that i had to have my buddy mig weld a bead on several ports and used a long auto body file board, with 36 grit paper to get them to seal. It took a long time sanding on them and several pieces of 36. but it sealed good after that!
Just throwing a few strokes with a file board will show your imperfections.