Well I started with the tube method and thought it was isolated to the #5 cylinder. Found a smoke machine and tried to verify with that but had no luck. Last night tried the seafoam option and, despite what looked like a forest fire, got some smoke to puff out of the #5 cylinder behind the flange where the pipe connects. Pulled the header and took this picture. Pretty sure that's the problem. Now - I was going to weld around the outside of all three pipes to the flange, and the only junk head I have immediate access to (to bolt on during welding) is from a 3800. Is the bolt pattern the same as the 3.8?
I was also going to have the mounting side of the flange surface planed after welding.