Shaft wear happens when it is not getting enough clean cool oil, deposits build up on the shaft when you don't idle down after hard use.
A hot turbo shaft plus hot oil is a bad thing, the heat soak factor of the turbo sitting with super hot oil in it the issue.

If you have been running hot, the oil will be hot from both the engine and turbo (the turbo tranfurs a lot of heat to the oil), and on top of that the turbo gets super hot when it's been working hard, the whole idea of idle down time is to let both the turbo itself and the oil cool.

In just 30 seconds of idling your engine can drop it's oil temp down quite a bit, which means less of a chance of super hot oil breaking down and coking up on the shaft of the turbo.
Turbo shaft wear is what you are trying to reduce, and the cooler the oil is in the turbo, the less build up you will get every time you shut down.

Watercooling does help all this, but really the watercooling is more for keeping the turbo cooler when it's running, not when it's shut down, it will cool the turbo down faster, but still does nothing for the actual oil, which is what you want to cool.

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Veronica, my 85 760Ti