thanks,
don

- I'd guess 60% of header gasket leaks are due to folks not re-tightening their headers after the first & second heat cycles.
- Then I'd say another 30% of the leaks are due to warped or uneven header flanges or old gasket left on the head surface.

Most folks can't get a torque wrench on their header bolts anyway and it's hard to over-tighten a header bolt (3/8") with the smaller bolt heads and necessary small wrenches needed to tighten them.

Make sure the exhaust gasket surfaces on your heads are straight & clean - Get a light down in there and get a good look at them. Make sure your header flange is straight & clean (it's not unsual to find welding spatter or such from the manufacturer around the gasket flange). Be careful when slipping in the gasket and tighten them down evenly. Once tightened, fire the engine and let it idle for a few (3) minutes. Let it cool for 30 minutes. Re-tighten the header bolts evenly. Go for a ride, but don't WOT it just yet. Let it cool for 2 hrs. Re-tighten/re-check the header bolts again evenly. Now you can kick it - it now should be good to go without any header leaks! Then once a month thereafter, re-check the bolts after it's been shutdown for 2hrs; because you can....