Thanks for that David 
The leather belt I have is square in section, it was cut at angles and glued together, I have no idea what glue it was and yes it used to make a slight “clack” sound at first but now it is silent, it certainly runs as smoothly as a plastic belt, I know this because my previous lathe had a plastic belt and I certainly don’t have any problems with slippage. I wonder if this could be down to the type or softness of the leather used as I have seen some leather belts which are quite hard and smooth, this one is quite soft and almost rough cut. I have been using it like this for the past 5 years and so far so good
I certainly agree with servicing the headstock spindle on a regular basis, if you want it to last for any length of time and keep its accuracy I think it is essential. I also keep it very well oiled, another thing which is often overlooked.
Paul.