Is that based on experience ? Is it pressure that kills it or fatigue. Pre or Post 2002 manifolds.

I'm also not sure that a RS1800 manifold will fit under a Focus bonnet.

As I said, the plastic manifold is good enough for the FRS and several turbo conversions I know of. I'm only asking because I get the impression that many people offering advice are stuck in a pre-98 time warp with little detailed knowledge of the Blacktop and its components.