Header Bolt Sealant/Coolant loss

I have a 69 Dart 340 and added tti headers and new header bolts. It seems like I have a coolant leak from the drivers side rear header bolt that goes into the coolant jacket. I am losing coolant out the exhaust to the tune of about a gallon every 10 miles. There is no coolant in the oil and none leaking out the bottom. I was going to pull the header bolt and use a sealant to stop it up.
I am sure I am not the first to have this issue. What do you guys do to deal with this?
1. If you use a sealant, what kind do you use?
2. I have had a hard time finding a sealant that will handle extreme temperatures. I have found a couple sealant that go up to 400 or 500 degrees, but I am sure the temperature at the header is a lot higher than that.
3. What is the recommended torque for the header bolts?
What say you experts?
thanks!
Scott