IIRC XW198 is the oldest Puma in the fleet but there was once a XW197.
XW 198 was the oldest 330C. The OCU started with six aircraft, XW198 --XW203. Westlands had a 330 B or E to play about with and also to assist in the production of the RAF versions. Once 230 squadron was up and running the OCU went down to four.
XW 203 went to 33 Sqn and was nominated as a CAAP (Components Advanced Ageing Programme) aircraft together with one of 230s and some French machines. Their job was to fly a minimum of 100 hrs/month ????????? so that with suitable monitoring the component life of important bits could be extended for the benefit of the civil market. XW203 failed miserably when it attempted a low level barrel roll as a result of something quite seriously wrong with the autopilot.
The fireball from the overload tanks in the back went between the pilot and crewman and conveniently removed most of the cockpit structure enabling them to exit straight ahead with only minor injuries.