Starter motor toast?

[John Winkelman]

The starter motor on my '87 5kCSTQ  w/ 170k miles suddenly started being
VERY noisy the past several starts. It starts the car okay (for now) but
sounds sort of like the bearings are being ground into fine bits while it's
doing it. I assume it's the bearings and not the brushes, since it does seem
to turn the motor over as well as ever. Any other thoughts before I get out
and get under (as soon as the rain subsides)?

jwink