I have two turbocharged cars. One with about 150K on the turbo the other is approaching 100K. Both vehicles get whatever synthetic oil is on sale in the proper viscosity and at reasonable OCI. Neither car is driven hard and rarely see max boost. Use mostly Shell high test gas. I have never had to change a turbo. I know they are expensive and in the case of the Saab with the exhaust close to the firewall, difficult to remove/replace. So how long should they reasonably last?