I agree with Wolf,

You have a compound problem, easily corrected.

First; don't worry about bubbling the swash perfectly level. Perfectly level doesn't always equate to perfect flight characteristics.
Adjusting the elevator servo arm out a couple of turns or so will fix the backwards problem (if Your battery is seated properly all the way forward and You are putting the battery in the same way each time).

Then, adjust the pot. If You can't get it to stop and the pot's maxed, then replace the motor; simple as that.

Simple as that, if everything else isn't contributing to creating alot more resistance to that particular shaft; end play, gear mesh, etc.

Gary.