Bigpants
The current propellor has not experienced any airworthiness issues, you can hardly black the aircraft because of different propellor built by another manufacturer that was not the item recommended by Grob and fitted at the RAF’s request.
I simply don’t see the aircraft as old and broke as you put it, I see a half life airframe that could use an avionics upgrade to increase reliability.
As to the cost of more military maintenance just take a look at the VGS vs civil gliding clubs. Military maintenance may be appropriate to fast jets but it is expensive overkill when applied to light aircraft.