Exhaust gasket keeps blowing
 

hey guys, i've just blown my 2nd exhaust gasket in 2 weeks, i don't know what the problem is to keep causing this, i've got the washers perfectly with plenty of presure on the exhaust side, as i have extractors, anyone think it could be from a non flat extractor manifold, mmmm dunno what to do

<font color=blue>76 260z</font color=blue>
The NiteRider