Another possibility is the starter motor could also be dry and corroded inside, this can prevent the starter motor pinion from travelling fully out.

This I believe is my problem so I'm changing my starter motor today. Sometimes it starts sometimes it won't when it does start the starter motor takes 4 seconds to turn her over otherwises it doesn't start or turn over just here it click at the starter motor. I did flood my car out in the mud now I'm chasing gremlins. Could just be an earth issue though