so taking that into account,
it's safe to say that the cracks formed after the initial tune from CRD that wasn't a good tune to begin with. Then problems with the tune started to escalate until Pete had enough and told CRD to stick it and decided to see Jez who had gone through a proper diagnosis checklist and found some problems and the cracks in the manifold?
Again, sorry to hear about your misfortune with this whole build Peter. One day very soon it will all be over and you'll be able to drive happily everyday.