Theres a much easier solution! I know you already have the gears but why not just do it right, associated makes plastic gears for their 1/8 scale vehicles that are a direct fit.
Plastic spurs for the RC8 series are pretty cheap and work very well. I run them on my RC8Be and RC8Te and they hold up great. A year ago I bought 4 of them for each car and still on the first one in both of them.