The problem we have is that the MOD didn't procure enough spares to account for those parts returned to 3rd/4th line or that the contract was never set up correctly in the first place. We used to have to rob tyres from one aircraft to fly another. Thank god that ridiculous position has passed.
One of the good things to come out of clearing out the Depots is the discovery of long lost things. Merlin Engine at Stafford, WM20s at Carlisle and a few years ago a 1940 Bren from Portsmouth.