longest owned by one owner
Sav, SMDJ is nothing! Here are a few which spring to mind which date further back.
* B206 G-CPTS has one owner from new in 1980.
* Norman Foster's B206 G-BKEW is close, he's had that since 1982
* WPD (ex SWEB) have had B206 G-BARP since 1982
* Alan Mann Hc B47G5 G-BBRI - while it has had three registered owners, the changes are nominal and AMH have operated this one from new in 1975 (including recent years as a hangar queen!)
I am sure there are more. No doubt the big operators have had some of their fleet for a long while - Bo105s perhaps?