VX275
I think one of the things Engines was alluding to (correctly) is the requirement to show x years (usually five) useful life from an investment. Before the grounding, an upgrade would get through scrutiny. But not after announcing the OSD. Related to this, support funding gradually decreases over the last five years. Only safety related work is permitted, and often not even that. Thus, if a replacement programme is delayed, both need a hike.
Engines
At the risk of repetition, if the paperwork is not right, an aircraft is non-airworthy. It is unserviceable. You don't know what its material state is. For the ATC, this was the end result of a long period of bad execution of basic engineering and airworthiness management responsibilities.
Needs to be said more often, until someone listens. Excellent post. Interestingly, the MAA witness at the Cunningham/Red Arrows trial in February disagreed. A clue to MoD's woes.