Well it hasn't worn out due to the hardened gears and carbide diff balls. I'm afraid if I loosen the diff it will increase the problem. Remember, I can't increase throttle in a straight line without it losing traction in the back-end. I can only guess that that's because one of the two wheels is starting to pick-up speed over the other. I'll try to loosen it but I really think it's not tight enough; I would even prefer locking the thing.