Be careful when buying the correct Burgess air filter box Paul. The late NH one is specific to those models I believe. I have attached a couple of images of my 1957 NH filter which will be what you need for your 59 NH. Take note of the cut-out where the air filter rubber connects as it goes up and ...

You have a bush type chain. When you change it get the much better roller type chain as less friction and longer lasting. The bush 'rollers' can split open with wear etc.
Regards,
Keith.

Of course Roger is right with respect to the frame numbers which correctly determine the model year.
Best wishes,
Keith.

The registration date would not matter as a new model may languish in a dealer's showroom for quite a while. It would be the date of manufacture that determines the year model. According to the Draganfly Ariel VIN information (downloaded free from their site), the model year starts the previous ...

Hi, the rear brake cable adjuster is assembled correctly according to the Ariel Owners Guide Appendum for 1957, see page 43 where there is a clear picture of it.
All the best,
Keith.

Hi Tracey,
Your Leader is still shown on the UK DVLA system as follows :-
DUJ 39C
✓ SORN
Vehicle Details
Vehicle make ARIEL
Date of first registration June 1965
Year of manufacture 1965
Cylinder capacity 250 cc
CO₂ emissions Not available
Fuel type PETROL
Euro status Not available
Real Driving ...

I think the guy you are after is Robin Arkwright who is a member of a couple of Ariel Facebook groups. He seems more active on the Ariel Motorcycle group but is also listed as a member of The Ariel Owners Motorcycle Club group.
Regards and a Happy New Year,
Keith.

Attached are some wiring diagrams Terry in which you will find Leader and Arrow ones. Hopefully you can open PDF files. Regards,
Keith.

Here is a copy of an Ariel factory document dated 1958 that gives torque figures, just convert them :- Best wishes,
Keith.

Hi Oliver, Draganfly list the non-FERC open type of rear chainguard you are looking for. Not cheap though. Here is the link :-
https://draganfly.co.uk/shop/70503/chai ... k/#5720-56
All the best,
Keith.