As a preventative measure, pre-winter, I pulled the starter on my '90 Bonneville and replaced the brushes. As I expected, they were worn almost to the brush holders, and it was just a matter of time before they caused me grief.
(Using the same techniques, I got 16 years out of the starter on my old '72 Olds 88.)
As it was, one of the holders was cracked. I might have pushed it over the brink tightening the little brush screw. In any event, the entire kit from Napa included the brushes, holders, springs, brackets, etc., etc. for less than $3.
The kit had to be special ordered! I don't hear of this being done very often, and I have to wonder why. It took about 75 minutes or so, and it's a rather dirty job, but the alternative was to buy a new starter at some inconvenient time, + probably a tow job, + the R/R job in vicious weather.
Why is it so rare for people to R/R starter brushes?? I was saving about $130 (+ probable towing fees) for less than two hours of work. Who makes that kind of money?!