I am talking about cutting the flange surface out between the center and rear sections of the exhaust manifolds. This was very common for me to do on the Mopar turbo manifolds to prevent bolt breaking and leakage at the rear ports. Heat expansion difference between the flange link and the manifold tubes causes them to take permanent heat distortion. My manifolds are showing about .010 low on the rear bolts compared to the center section of the flange. I will resurface them to straighten them out, but no reason to believe it will not happen again.
The manifolds have center holes tight to bolts, outside holes bigger, which is typical if they expect them to be able to slide as they heat up and cool down. That also means that the gaskets have to allow that and would probably explain the double thickness embossed steel stock gaskets, to seal as sliding. The bolts also have to be just right so they allow sliding but be tight enough to seal, so lots of balancing out to work.
The turbo engines would pop the heads of grade 8 bolts like nothing, and even grade 5 would sometimes not be flexible enough to never break.
I finally started using grade 8 strength stainless bolts, which did work much better. The stainless expands faster than steel or cast iron with heat, so they slightly loosen as the get to temp to allow some sliding, and the high strength allows good cold clamping force and enough at high temp, it appears. The loosening also releases some tension in them so less likely to break.
I think I am going to use 12 point flange head, 170k stainless, bolts. Am not sure on gaskets yet, but may go OEM unless I find something more certain.
Probably will cut the rear flange link out, too.
Both of the gaskets showed rear bolt area leaks, and it did have a noticeable tic when cold, and manifolds are warped, so some remediation and improvement seem to be in order.