You've hit the nail on the head Loneworlf 50,
The UK's Apaches are going to suffer from serious obsolescence issues in the near future due todifficulties in sourcing many of the aircraft's line-replaceable units.
As technology progresses, these LRUs are simply no longer going to be procurable.
The main issue is with the aircraft's processing suites, which comprise a systems processor, weapons processor and a mission processor that are subject to Moore's Law - "computer memory is doubled every six months".
Therefore, the chip manufacturers have a very small window where the chips are viable before they stop making them. To try and counter this obsolescence Boeing engages in what the company terms 'last-time buy'. Under this initiative it sets about buying all of these chips as the manufacturers decide that they are no longer going to support them.
Even so, this is still a finite amount of chips, and they WILL run out!
To try and counter this, the MoD's unstated intention was to skip AH-64D Block II and go straight to Block III (now AH-64E), but that was before the economy went to hell in a hand basket. Who know what they can afford to do now?