WL679
This was actually a Farnborough aircraft, one of 3 Varsities operated by RAE between mid-70s and early 90s.
WL679 was a FLIR research aircraft so its presence at Gutersloh was unlikely to have been just for refreshments. I recall 2 weeks at the same place with the same aircraft in the early 80s chasing tanks etc. Much fun.
lm