By the gearbox I mean the part of the transmission besides the belt, like for instance when you go into reverse. I never hear of problems with them on Polaris quads so I am assuming that they must be ok.

 

Other than putting a hole in mine when my chain broke, no problems. I like how they are seperate from the engine, so if you need to work on it or remove it, you don't have to pull the entire motor. The downside is that it's a pain to get out.