Since the original center gear is made of plastic, so it is easily worn out.
For the problem of servo failure to return to center position,
1) Pls check whether the servo screw is too tight, if yes, lossen it a few turns or remove any 介子
Or
2) Check whether the steering parts are too tight by removing the servo, and then see whether the steering parts can be moved freely, if not, then check your steering parts.