Servos have never been replaced. Unit is a little over a year old. It started doing this a few months ago. Not very often. I would plug it into the charger over night then it would be good for a few sessions. But now it seems to be happening more often than when it works right.
we had this problem a year or so ago - but I have no idea how my hubby fixed it. He is MIDTNGRNHEAD on here. Search his name - I think he was the one that started that thread, or you can PM him. I'll try to remember to tell him to look at this and reply.
Reversing the wires won't fix it. BB use a true servo signal to control the direction. The width of the signal determines the servo position. You might try cleaning the contacts on the main plug or replacing the servo.