This 1973-4 Jazz Bass had a custom fretless neck made in the mid 70s , (not by me) and I got the neck, pickups, and assorted hardware, cut to 2016, guess who walks in the door! Time for some work, seem the low E string sound is cutting out on the neck pickup and the strings are sticking when being tuned. Well as you can see the nut had about 30 years of grime and goo and needed a good cleaning and polishing, good as new.
Next to the pickup, it turned out to be the sponge which was used back in the day by Fender instead of springs had turned to baklava! It was sticky, wet, gooey and crispy, gross. And it was apparently shorting out the exposed Bartolini pickup leads, check out the pix. I cleaned everything and replaced the sponge with Nora Lunalastik, (an orthotic material), and voila, low E is back!