The original oil line fittings had a nut that compressed itself into the copper line- - - - -no compression sleeve. It was a one-time use item. I recycled the one on the 216 I just put on a run stand in the school shop by filing off the extended part of the oil line flush with the nut, and running a 3/16" drill bit through the original nut. Then I installed it onto a new piece of copper tubing and tightened it into its original fitting on the engine. Sometimes it's possible to re-use the nut that way, but usually a new nut must be used if you can find one. It was once a stock item in the Dorman fitting assortment at every LGS. I haven't seen a new one like that in at least 20 years.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!