Thanks guys - I'll be pulling out over the weekend and having a look at it and see what the deal with it is... I'm hoping it is something simple like a leaking fuel bowl, or dirty contact !

if you have trouble finding one you can take yours to a guage specialist an they will rewind it for you.
Like any variable resister the constant movement of the senders arm on the resistance wire will finally wear through the resistance wire.

These things are usually very good, but i guess one will fail every now & then. The only real fix is to replace it with either a new one, or a serviceable used one.

They are not a "high demand" item, so you should get one from a wrecker quite inexpensively.

The fuel gauge on my 120Y is not working and I've tracked down to the sender unit in the tank (I earthed the sender wire and the gauge immedately read full). Do these things have a history of failing and is it an easy fix? I've already checked the connection of the sender wire to the terminal on the sender. Any information would be appreciated.