have switched their rear-drive cars over to FWD type sealed ball bearings for reduced rolling resistance, but if you had such a machine, you'd know that they can't be serviced, only replaced.

Autozen is right, though -- way back in '69, Porsche changed their service philosophy to eliminate scheduled wheel bearing repackings (except when the hubs had to be taken apart for other reasons, such as brake work) on the grounds that almost all the failures they had encountered came from botched repacking jobs -- usually dirt -- rather than dry bearings which had not been touched since they left the factory.