I have a scag 36 belt driven walk behind mower. The mower wants to do circles. what I found is the right side output shaft coming from the gearbox moves slighty outward and causing the shaft to not make complete contact inside the gearbox. With the mower off and in gear I can turn the shaft and feel that it's slipping inside the gearbox, if I push the shaft in all the way it feels fine no slipping. Is this a common problem, and is it an easy fix?