I would like to replace the rear air bag E500 Sport where do I purchase ?

Arnott offers a replacement bag which is cheaper. It does not have the air storage tank which is not really needed. Book time is approx 5 hours. IF you are using an arnott bag, the time should be closer to 2 hours since the subframe does not have to be dropped. Make sure your shop has proper tools (star diag) to properly inflate bag to certain pressure before lowering car or the airbag will touch the drive shaft and develop a hole.