Fortunately, even the though header flange wasn't completely flat, the gasket "squish" was sufficient to prevent any leaking. There also were no leaks at the overpipe to front pipe connection. However, there was a big leak at the annoying header to overpipe slip fit.
This last weekend, I made my third attempt to seal the joint. I removed the overpipe from the header, cleaned the connections, and tried using the permatex copper high-temp rtv sealant this time. The below videos are me thinking I finally sealed it - and then realizing there was still a small leak.
[ame="https://www.youtube.com/watch?v=uYA0TWSAOXs"]IMG 1867 - YouTube[/ame]
[ame="https://www.youtube.com/watch?v=NFOloYLdXJo"]IMG 1868 - YouTube[/ame]
I tried plugging the top leak with Permatex Muffler/Tailpipe sealer, but it didn't work. I've officially given up for the time being on trying to fix the leak as it is pretty small. My next attempt will likely be with a stepped exhaust clamp like this:
http://www.jegs.com/i/Dynomax/289/33...SABEgJy9PD_BwE