At April 2011, 43 Sqn had 84.00 years service and 111 Sqn 83.43, so it was a close call.
The only flies in the ointment are 25 Sqn with 91.11 years and 23 Sqn with 87.08 years - but then 43's Scottish connections seem to favour it. (Source UK Air Power 2011, Key Publishing.)