Try NEP still in Aerostich catalog. Cut grip off, have spare on hand. Idea to to make work smoothly. I drilled NEP, use either safety wire or thin nylon tie to steady tab in between the 2 throttle wires.
Replace grip, making sure space is left so there is not constant friction with rotating grip touching NEP. Adjust friction you want/need with NEP. $20 or so total cost. Seem to work forever, great for wiping nose, break on wrist.