Took a little longer than I hoped as I originally bought M7 which was a sloppy fit. Got this
https://www.ebay.co.uk/itm/361393790411 Which did need a bit of playing with - a small bend out of the curve at bottom of the J. I also had to slightly enlargen the guide holes to accept the thickness of the thread and extend the thread by 20mm. This was for an El Tigre seat so needed shortening by about 20mm.
I had a spring from a Xmas cracker in my 'that'll come in handy box' because I am soooo middle aged & dull! Seams to work well and adjusting by the nut stops the many Spring nips my fingers get when faffing about with the split pin adjusting set up.

I've not tried in the scooter yet. Before that is there any special technique or order to attach the seat cover tabs to the base please?