I wonder if the Whirlwind accident was what prompted the rules about Royals flying in Mil helicopters - the Royal Flight ones ISTR could not have any components that were past 50% of their expected life and the same rules were applied to our Wessex in Cyprus when we flew Princess Anne back in the 80's.
Yes, we used to change any component on the VC10 that was over half life, additionally the Queen had her own set of wheels, in the days of trend logs I often thought it stupid to pull engines and fit totally unknown quantities in their place. Additionally we would retrim / refit the cabin with the Royal fit, she also had pure wool gold coloured carpets throughout. The exterior would be hand polished and a prep would take up to 28 days including a spare without the cabin fit in. It may have been a lot of expensive bulls*it but it did keep the fleet up to a good standard, it wasn’t unusual for one to come off a Royal then go down route carrying freight.
if you remember the Andovers with the highly polished undersides on Queens flight, they found they had polished so much metal away it needed reskinning work and then was painted light grey underneath.
Not just Charles and William, but William and his son too BellRinger.
Re the Whirlwind wasn’t it cracking of the “Jesus nut” I seem to remember it was a known problem and there was a NDT procedure in place but tragically the time it took to appear to total failure was less than the time between inspections.