[jeffko]

Chris, I had to retorque my manifold bolts 3 times before they finally held the correct torque amount. I think the last time was when I had 250 miles and they were off by 5 to 10 lbs. There is seemingly a lot of crush in those gaskets.

What I'm saying is that you could be loosing your seal due to insufficient compression on the gasket or enough loss to allow erosion of the gasket. The only thing else I think it may be is a warped surface, which is possible but doubtful.