I installed new exhaust manifold gaskets about 4 months ago (1955 Tbird 292).   I tightened them down and after running it a couple of times I tightened them again.   I checked them this weekend and a couple were not tight, they needed 1/8 of a turn.   I heard if you tighten them too much the manifold could crack.

I obviously have to go a little tighter, is this common?   I thought I read someone else had a similar issue.