Hey Billy, I own a 78 Series bass and it also has a solid brass nut, The adjustable nuts were a later development.
Sounds like either you need to check the set-up on the bass and adjust to taste or you may have a high fret somewhere. Can you tell where on the neck (low, high or somewhere in the middle) the buzz occurs? I know this is harder when it involves an open string but would be helpful in figuring out what is up. Does it buzz if you pluck/pick near the neck or does it buzz wherever you pluck including near the bridge?
Also, if the strings are old or you just got a wonky one, that can also lead to issues. I am sure you will get other feedback, good luck getting it sorted out...