I second the suggestion using Remflex gaskets.
The remflex gaskets sealed a stubborn leak between the header-overpipe and overpipe-frontpipe connection.
Pay attention not to bend them, because they are fragile when subjected to bending stress. They compress slightly when you tighten them (torque the bolts/nuts according to Remflexes torque specs) and fill any flange imperfections.
I ordered the gaskets directly from Remflex (Mrs. Diana was my contact) and they provided me with reasonable shipping costs to Slovenia (approx. 40€).
Since I'll be needing another set of their gaskets, we could make a group buy
Cheers