My current brushes are in poor shape after 14 years, I have new ones on the way but was curious how complicated these are to replace?

I am referring to the two that are connected to the pillar garnish (outer brushes), not the inner brushes. see photo below

 

I am in the midst of doing my top. I think for the outer brushes you have to order the drain tank assemblies that have the brush on them. The brush is riveted to the tank. You'll need to take out the top to put them on. Might want to save fixing until the top needs it.