Is there any issue with using the switchtronic system 90% of the time I drive (mainly urban and occasional motorway driving)? Or is the switchtronic system meant for occasional use?
As probably 90%+ of MB owners with automatics (including me ) leave the transmission in Drive except on rare occasions I expect the design of the gearbox might reflect that. On the other hand, I can't see that you're going to harm the transmission by using manual control.