That’s my experience too. Very minor leaks in threaded fittings usually seal themselves after a while.It's leaked, It's probably sealed itself by the looks of it.
My grandfather used "cotton cloth strips" wrapped around" weeping joint and then tied off. This in the day when pipe dope and Teflon tape was not "known" to the general public as it is now. He was born in 1903 and passed in 1984. He knew a lot of "stuff" that worked and probably would be laughed at today. The cotton strip does work...try it and I think you will be surprised.
