Here is an excerpt:

Toby

ok so you will need to unbolt this of the front of the of the pedestal. you will also need to loosen the chain so it can be lifted of the sprocket.
once this is done you will be able to remove the input shaft and then the rest is easy.
there should be a circlip front and back
once these are off it is easy to remove and replace any parts that are an issue

Client

I have unbolted it from the outside, and the white surround does not move at all. (But I have not loosened the chain yet. )
Did you see the photos I uploaded? One shows a bent washer behind the inside circlip. Could that be causing my squeak?

Toby

yes it could well be coursing the squeek.
i have just looked at the photos thanks
the chain will make this hard to remove until the tension has been let off.

He also provided some helpful diagrams in PDF form, and he said it would "help" to remove the fiberglass surround. (That might be the biggest part of this job.)