Exhausted with Header Leaks

I've always found that both the header flange and the head must be fully clean and prepped before install. Final cleaning with acetone. Wear gloves so crud doesn't get on the gasket, head or header. Cutting the flange like stated above helps. Ive used a high temp copper spray that is sticky that helped installation, probably long term seal as well. A retorque of the bolts/nuts after a couple heat cycles is necessary. Retorques every so often if you have problems. An actual retorque, not just "tighten them up." Quality gaskets are also helpful.