FWIW, back when I used only teflon tape (not the Permatex Aviation Form-A-Gasket), I sometimes found that the joint still leaked, even after I had tightened the fitting as tight as I dared to tighten it.
When this happened, sometimes (not always, maybe not even most of the time, but sometimes) I found that if I backed-out the joint maybe 1/8 turn, sometimes that would seal it. My theory was that maybe the teflon tape, after shredding, was "jamming" between the threads when I backed out the fitting a hair.
Anyway, FWIW and YMMV and it might be worth a try if/when all else fails.