header flange bolts
Do you have headers or the stock cast iron manifolds? If headers, who made them, Thorley, Gibson, Banks or? Do the nuts actually get loose or is it just that the gaskets start to leak? If the nuts are actually coming loose, I've never heard of that but if it is just a leak developing then it may be that you need new gaskets and or manifolds. A leak can make a cut into the seat to where it can not be tightened enough to keep it from leaking.