Starter motor itself is rather robust, contacts for the solenoid not so much.
I have 216,000 miles on my M. 1 set of contacts and still going strong.
Kind of a DIY guy repair. Most shops would replace the complete starter motor.

 

To tell you the truth the size of the engine and placement of the starter are intimidating. The thing us it just started making no noise at all out of the blue when we turned the key over. No grinding or any of the noises a starter makes when going out.