Early on I believe that many of the Cat 5 airframes were stripped for spares. I saw at least 3 airframes which had been stripped back to absolutely nothing (shells). These were then sold off by MoD tender.
I was told that the logic was that no spares forecasts had been completed for the airframe and no spares ordered (not an untypical situation with an end of year splurge 'use it or lose it' accounting system which was where the original funding tranche came from), which meant that any items that needed to be replaced (other than wheels, tyres and brakes) had to be special orders from Grob. During the first third of the airframe life Grob announced that they were not going to make gliders any more and focused on Powered aircraft. Items from Cat 5 aircraft such as control columns and airbrake assemblies, seats, straps etc were certainly reused in other aircraft.
This meant that the spares source effectively ceased, although Grob would make spares on a 'one off' basis at an exorbitant price per item.
Later some Cat 5 airframes were BER'd and only partially stripped - others sold in an 'as is' condition (such as the trailer accident). These were probably repairable but not cost effective to do so. As we know - anything is repairable if you throw enough £ and/or skill at it. Since there was a glut of Vikings at this stage (due to basing strategies meaning that many Viking sites were closing) I assume it was decided to reduce the overall numbers anyway by releasing the damaged airframes.
In parallel MoD was hunting down civilian Grob 109's that had been built at the same time as their own and purchasing them at above market rate and then having Modifications embodied to bring them to the same level as their existing fleet. These were then issued to VGS's to replace Vikings at sites where the Viking was no longer 'acceptable' to the unit basing strategy.Hence the increase in Vigilant Numbers overall and reduction in Viking.
WRT to sales of Vikings - These sales were all by the usual MoD Tender system as far as I am aware. Maybe the RAFGSA just got lucky (or unlucky !!).
Arc