Vauxhall Corsa clicking noise when starting / starter motor

When starting the car up it makes a clicking noise, the car always starts first time and is running fine, one day it can be a loud clicking noise and then next day it can be abit quieter, can leave it standing at work for 8 hours and it will sometimes make and noise and then the next day it wont, have been told by my mechanic that it could be the starter motor and have told me to leave it for a couple of months, he really doesnt want to put a new starter motor in and could still have the same problem, it has already been going on for a couple of months. Any advice would be great?