XRAY - Model racing cars

When I apply forward throttle, a one-way should automatically apply forward action/traction to both wheels. When off throttle then the wheels should freespin. If I apply brakes then nothing should happen. All this occur when I have very slow forward throttle and everything works as it should.

The problem occurs when I apply a lot of forward throttle. At high RPM, the left wheel spins very well. However the right wheel starts spinning a first then it kind of slips and does not go forward anymore. I can just grab it while the car is in full forward motion and hold it while the left wheel madly goes forward.

After closer examination I noticed that the outdrives looked dirty...And that the diff case had a little oil? residue. I decided to wet a Q-Tip with a little motor cleaner (very little) and cleaned the inside of the diff with it. This solved the problem. I suspect some small residue would have greased it just a little and when high RPM would hit, it may slip and once i had it would remain un-engaged. I will give it a try on the large track (bigger then my basement) on Wednesday and test it fully...