D6-9U Dripping top bleed valve

This is a nagging problem that started after cleaning the fuel filter 'tower', (and rebuilding the fuel transfer pump)(Also changed the two seals between the filter housing and the fuel injection pump) Anyway, the line that the top bleed valve, (the one with the round finger tightening disc), doesn't want to shut completely off. At least that seems to be the only place that could be allowing diesel to drip from this line, which terminates at the bottom front of the fuel filter housing. No amount of tightening will stop the 'drip'. Have had it in and out two dozen times and tried various alternative 'fixes', including o-rings. Also replaced the brass 'disc' at the seat of the fitting. No luck.
Has anyone had this problem before?
Perhaps the needle assembly is worn past point of no return? Have one on the way, just wondering if there is another potential source for this drip??

I think you hit the reason it,s leaking as the seat and the wheel are worn so a new one should fix it. If you have two sources draining into the one line at the bottom then take the line out of the top where your leak is and see if it still leaks up there and if not then could be the bottom transfer pump seals bad draining into that line.

SJ - Thanks for the idea of isolating the leak source; should have thought of that myself. Did not know where that second line sourced from though. I do have a second line that enters the bleeder line. (And I did work on the fuel transfer pump!) Since there was no problem before, it well may be that the pump seal(s) got shifted on re-installation. It has some tiny orings around the bolts that may be the source.
With diesel prices this drip adds up.
yellerc@