Thanks to all for the suggestions.
This looked promising but the bottom of the page lead me to > https://www.amazon.com/CATTONGUE-GRI...dp/B08CS3Q3Y4/ <
A wedge shape can likely be cut out of that to wrap around to make a continuous seam and do the job.
Thanks again everyone for the help.
Years ago there was a replacement set of all the grip rings for a Gitzo tripod on ebay, but it was for a different size tripod than mine. it would seem having spare parts for what is considered a top of the line tripod would be a good practice for loyal customers.
jtk