Also, if you have a tiptronic -
The Tip has an electronic coolant valve similar to the T'stat on the engine. This valve remains closed until the engine warms up to prevent coolant flow to the tranny so it can come up to temp quicker. Once up to temp, the valve opens allowing coolant to flow through the tranny.
You need to deactivate this valve before draining, flushing, filling and bleeding the system or it will trap air. You do this by having the key in the Off position and pulling fuse B1. Once the car is bled, again key Off, replace the fuse B1.
This does not appear in the Bentley, but is one of the steps in the factory repair manual.