Yeah its just the diff rings wearing in, this is normal.
As said above tighten the slipper right up, holding the spur and right wheel in your right hand you should be able to turn the left wheel just a fraction if at all, tighten the diff till ya can't.
Then losen off the slipper a couple of turns. repeat above but this time when you turn the left wheel the slipper pads should slip with the wheel, then fine tune at the track.
I read this in a losi manuel and have read similar on rc10b4.com so it must be true
