My 2015 1.6 diesel has recently begun to not start first time. The engine isn't cranking but there is a whirring sound as though the starter motor is spinning. If I stop and try again it usually starts as normal. I know the solenoid should push the starter pinion along the shaft splines to engage with the teeth on the flywheel, and the contact in the solenoid should close to energise the motor. Does anyone have experience in overhauling the starter motor? My thoughts are that it could be the pinion is sticking on the motor shaft, or the motor brushes are worn down. Any ideas?