The official line is as follows;
"The MRA4 is a new aircraft which has mostly been designed, from first principles, with modern design features and safety standards for all the main systems and components. Where MR2 design has been retained, mostly the fuselage structure, bomb bay doors and tail assembly; the components have been completely refurbished and re-lifed to meet the expected life of the MRA4.
A number of components have been retained from the MR2 aicraft that have been decommissioned. The Nimrod PT is currently undertaking work to assess which components from this pool could be retained for use on the MRA4 fleet."
DV