Check torque at the manifold screws into the head, and check that the collectcor nuts are tight. I'd replace the collector nuts while I was about it - they should be 3/8"-16, and I tend to use brass.
Those are the most common leaks going. Also, cracked headers seem to be accompanied (actually, preceded) by failing engine mounts - so make sure those are solid as well. If you have to change the header, change all three of the rubber mounts as well (two for the engine, one for the transmission.)
5-90