If you don't already have the four gear diffs, do that right away. I'm not aware of a whole diff that can be substituted. I think guys were using Kyosho spider gears until HPI released their four gear version, so they might be a little better. Most of the time, shimming the diff assembly to get a better gear mesh will solve the problem. Mine have held up pretty good without having to shim, but I know people who had to in order to solve breakage issues.