The Decca (Avionker is correct) was removed late 90s/early 2000s, which is about the same time as the EAPS (Sandfilter) replaced the old barn door above the cockpit. The other external detail to consider including is the large tail letter (one per airframe, omitting the letter 'O'
) which appeared in about 2005 although it took several years to apply these across the fleet (based on the rotation of airframes through depth) and at least one airframe never carried the letter.
In terms of 203 (R) Sqn aircraft (NB SKTU officially was pre-1996 and then again 2014-5), unit badges were carried some of the time on both sides of the aircraft (and, in one case, on the sonobuoy cover on the bottom of the hull). Typically, of the five airframes at Valley, three would carry 203 badges and two had 22 Sqn badges, as that was the nominal strength of the units, but in reality the aircraft were pooled. There was also a period when C Flt 22 Sqn became a bit too precious about flying aircraft with 203 badges, meaning that all 203 badges were removed for a while. This ended after a change of management and some guerilla badging in the hangar, helped by the fine folks of the Graphics section. Final detail: in 2014, the special 203 Centenary artwork was carried by two airframes for several months.