It sounds like it's time for a new starter. A flat spot in the starter refers to a copper washer in the solenoid that pits and no longer makes a proper connection all of the time. As a result, the owner experiences the exact symptoms that you described.
I feel that replacing the starter will solve your problem.
If you have any other questions, let me know and I'll try my best to help.
Friday, August 17th, 2018 AT 3:44 PM