This is (part of) what caused my transmission to require repair recently.
The first thing on the left is what one of the bearings was supposed to look like, more or less.
The middle thing is what one of the bearings did look like. This bearing went between two critical gears (not that there are extra, unnecessary gears or anything, but these ones were large and .. well, monstrously fucked by this bearing failing, among other things.)
The gear on the right is as you can clearly see, missing a few teeth. In this blurry picture you can see another gear assembly with lots of missing teeth here.
Anyway so that's the story. They had a whole box of fucked up gears, these are the ones I decided to take because they were the most obviously fucked.
I'm pretty impressed by the way machines destroy themselves if left unchecked. Things like this facinate me and I don't know why. :)