Hey never read that advice, thanks!! I did try a fat finger and noticed nothing, but not the truss rod.Sounds like you've had this for years so I'm assuming many different E strings and same issue. You might try getting a heavy C clamp and clamping on your headstock and see if it changes the overtone/dullness. Usually Fender necks have a goofy spot on the G string that can be remedied by adding or removing weight from the headstock. I had one with dull spots on the neck and switching to super lightweight tuners cured all the dead spots on that particular bass. Maybe it'll work for you E string.
Also ... I assume you've made truss rod changes over the years? Just mentioning that because it's possible the truss rod is just resonating in a certain way and maybe loosening it up and tightening it back up again might reposition it just enough to stop the issue? Wild shot in the dark but sounds like you've already tried all the obvious answers.
