Bron - DO NOT put anything on the skin.
If you try to "wet" the vellum it will stretch, and may split.
A banjo skin has to be HARD to hold the pressure which is transmitted via the bridge to a VERY NARROW section of the skin - i.e.All the pressure is where the feet of the bridge touch. The only time a banjo vellum is deliberately soaked is to initially fit it to the hoop. Once the vellum is correctly in place you take all possible steps to prevent it getting wet.
The term Zither Banjo refers to the 5th string disappearing down a brass tube and reappearing at the machine head. The original "zither" banjo was invented by Alfred D Cammeyer(1862-1949). The first design appeared around 1888. Two sets of three guitar tuning pegs is fairly standard. The tuner manufacturers didn't make sets with TWO tuners on a plate.
Cammeyer also played banjo and composed music in the "Classical Banjo" style. I used to play one of his tunes which someone found on sheet music, but I don't know if I still have my hand transcribed copy.
The manufacturer's name on your banjo doesn't ring any bells, but I am not an authority on manufacturers. I do know that a lot of banjos made by the Windsor company bear different names. My Great Grandfather's zither banjo - the one I learned to play on, is a Barnes & Mullins No.2. Barnes & Mullins sold musical instruments, but did not make banjos. Their branded banjoes were actually Windsor Banjos with a different name stamp.
There are numerous previous threads on 5-string care, maintenance and repair. The forum search will find you some interesting information.
Also Llanfair - If you wish to get in touch with ME (send a PM) I can tell you a lot more than fits in a thread.
Quack!
Geoff the Duck.