...when you wrap Teflon tape, you must do it in the direction of 'Tightening' as the plug is screwed in. The plug in the photo has been wrapped in the opposite direction, and will loosen as it is screwed in. This alone can account for leaks. From My experience, Many Machinists and Mechanics don't know this. And in Aircraft, the Minimum is 3 Turns. And be careful not to tighten the plug too tight, or you can Crack the Case!! Teflon tape makes it very easy to Tighten-Up the Plug!
My Plugs Never Leak.
Just My 2 cents
MJ
P.S. When I do the Oil Pan Drain Plug, I use a Rubber 'O' Ring AND Teflon Tape. NO Drips, And those Plugs Will Strip Easily!! The Designers Should have used a NPT, Tapered Thread, can be Tightened and near impossible to Strip. I Repaired a few Stripped Pan Drains, for 'jiffy Lube'. I would Braze-in a Brass Adaptor and use a Brass NPT Plug! Saved them a Lot of Money! And with Tape, Sealed Very Well.
Remember! 3 Turns on the Tape, Tightening!