PDC

Are the turbos on 600 and 65 series benzes 'closed' / 'internally lubricated' units, or do they draw lubrication from the cars oiling system? If they are closed - which is my guess - do they ever require maintenance? Just wondering how long the bearings and other moving parts are expected to last. They see pretty high rpms and heat while spooling. Might be nice to drain and fill whatever lubrication they rely on.