Bill
On a longstroke & poss others (I only know Perkins longstrokes) there should be a fibre washer between the the banjo & rockerbox.
There should not be a metal washer, cup or otherwise on the outside as yours appears to have.
If that is a washer between the bolt & rockerbox it would appear you have incorrect bolts as they should like those posted by e.
The bolt is a taper fit forming an oiltight seal.
But it would appear that what you have is a pattern banjo not a brass with copper pipe original, so who knows how it's mean't to work, obviously doesn't though!
Will post a pic of correct banjo in the morning if someone doesn't do first.
What happened to the previous one you mention?
Rusty