2012 Volkswagen GLI - how do you know there's turbo trouble?

What are the symptoms of turbo trouble … have you had any issues with coolant leaks?

Turbo’s can leak oil which is identifiable by white smoke out the exhaust and higher than normal oil consumption. Failed turbo bearings can be noisy when they fail but you will notice a drop in power before you can hear it. Modern turbos are quite reliable and can last for well over 100K miles.

I don’t own one so I can’t comment about coolant leaks.