I am have a leak on a new bathroom sink I have just installed at my relatives' place.
It occurs just below the slip/jamb nut, but above the pivot rod assembly.
In the picture, the threads appear white (because there is teflon tape on them. I forgot to teflon tape the entire thread, as there is no tape under the slip/jamb nut or above it). You can see the water droplet in the red square box where the leak is occuring.
I used the foam gasket that came with the fixtures. I wonder if that could be the culprit.
The question is, what is the best course of action? Tighten the slip nut? or disassemble all drain components and retighten/retape / apply plumber's puddy in place of the foam gasket that is under the flange.