The only time I've seen teflon tape or thread sealer used on flare fittings is when someone uses stainless steel lines. As most of you know, they can be a bear to initially seat and seal without drips. I think many folks do it out of frustration. The slick setup for stainless fuel lines is a copper insert that goes inside the flare. A mechanic who retired from a Caddy dealer after many years had a bunch in his tool box. I don't know if you can still get them anywhere but they sure made sealing up a 427/435 vette with stainless fuel lines pretty easy.
