Thanks for your interest in this topic
This header runs 4 into 2 into 1 and then out through a hole in the body. It one cracked on three flanges: just the top on two and three, completely on four and number one remained ok.
The exhaust is held in two places: as it attaches to the exhaust ports anyway and again on rubber mounts on the body work back from the err, 'silencer' (ehem). So I imagine this unsupported mass over-stresses the flanges.
(The seals have been sound and perhaps this is because of the looseness due to the cracks)
I am tempted to take it to 'TubeTorque' - or the like - and get a quote for one made up, if the originals are quite poor, but thought I'd consider more inovative and economic solutions first.
Nat