I just pulled a starter off my Perkins Engine that had sat for 32 years. The starter looked good on the outside, but when I pulled it apart it looked like Mars...the red planet! It was nothing but rust! Undeterred, I pulled it all apart, and spent four hours cleaning it up...
Then, as I was sliding the housing back on, it hung up on a brush, and that 42 year old bakealite holding the brush, snapped. All that work, and I still had to take it to the repair shop. In the end I found I could buy a new starter cheaper than I could rebuild it, so I did that, but it would have saved me four hours worth of work!