I think it's the opposite maltreatment of engines, from low to high power when the engine is too cool that causes the most damage. Applying full power from the end of a long glide or having done the incremental long cool down of your Navajo, then suddenly applying full power such as in a go-round. It's better to keep the temps up and cool down taxiing in once on the ground prior to shut down.
The other thing that will do a lot of damage is rapid throttle/rpm changes that throw the engine balance out. I would add excessive vibration to temp and pressure as engine killers.