every time a OWB slips it wears on the OWB shaft, which is why often times just replacing the bearing doesn't help much........ when a Owb starts slipping you need to stop immediately and clean it...people who insist on trying over and over will just do more harm then good....... myself as soon a OWb starts to slip I flush the engine with WD-40, let dry for 5 minutes, the usually the bearing grabs right away........ As soon as you feel slip you need to stop, hammering the rotostart over and over just wears the OWB shaft.......