How to replace FST Driver

I recently began to hear distortion in the midrange of my B&W N804s at certain volume levels. When I press lightly on the midrange driver, it clicks/crackles. I think the driver is blown, and that I'll have to get a new one from B&W. Does anyone know how to remove the driver and replace it? I intend to call B&W, but thought you forum folks may have some tips. Thanks.
Go to this B&W site and download the service manual for your speakers:

In my experience these service manuals are sufficiently detailed to be able to work out how to do a repair.
I did. However, the manual doesn't show what tools, if any, are needed. For example, when I loosen and remove the large, silver screw cover (which is supposed to hold the midrange rod in place), everything remains tight and the driver stays in place. It looks like there may be a special, hexagonal screwdriver necessary to loosen the rod, but I don't know where to get one. Also, the is a circular, brass piece with a rubber gasket that does not appear to be easily removable.
UPDATE ... Success! I called B&W and they said the rubber surround might be sticking to the front of the speaker because of age. So, SWMBO suggestee that I use the eraser end of a pencil to push from the back and exert a little pressure. Bingo! The driver came out and I've ordered new midrange drivers for both speakers. A pencil eraser ... go figure. BTW, tech support at B&W is very helpful and knowledgeable.