Impaseo - Once again I am in general agreement with your comments, but the final paragraphs concerning criticality are a bit difficult.
A Critical Part is one the failure of which could cause Catastrophe. I do not believe the Requirements or Regulations provide for levels of criticality. Parts are either Critical or not,and the lifing and manufacturing processes are applied accordingly.
If the safety assessment indicates that a non-disc type part such as an oil pipe could fail in a manner likely to lead to Catastrophe a redesign would be necessary. Hence engines have few Critical parts other than discs or shafts.
I also have difficulty with your view that the current rules are sufficiently robust to be able to encompass 'lessons learned'. My experience indicates that if your really believe safety needs to be enhanced then the only certain fix is a change to the Rules. Tinkering with advisory material seldom works.
It has to be said that the whole arena of safety assessments is an absolute nightmare when it comes to agreeing compliance, since there are so many different ways in which the job can be done. This inevitably leads to inconsistency of approach between constructors and between regulators.
Perhaps it is time to stop assuming that everything on the aircraft is correct to drawing and adopt a more pragmatic approach that recognises human falibility, such as is the case I believe with CRM in operational affairs.
Trouble is, Regulators are not very imaginative when their fundamental assumptions are challenged.
Sorry this is a bit rambling, but it's quite interesting, isn't it?