[Fat Charlie]

Damage spreads.

One thing gets a little loose and rattles around. The more it rattles, the harder it hits, causing more damage and allowing itself more movement. It uses that space to hit harder, and next thing you know things all over the place are taking hits.

It's a bummer, on that D-60 you've got two pinion bearings, plus the pinion seal. Only one bearing's shot now, but every revolution is taxing the bearing that's left.