Replace the brushes now while you have it open, so you don't have to do it again later on. That's what Les is trying to say.
Because as you seen with this Kirby, you never know what a vacuum has been put through by the previous owner, and more often than not (at least in the USA) vacuums are run into the ground and then some before they are donated or trashed. Better to replace everything now while it is all laid out than to keep opening it up repeatedly every few months (you can actually strip out the threads in the screw posts on plastic bodied vacuums by unscrewing the screws too often).
It's just like when you buy a used car, you replace every high-wear rubber part (tires, hoses, belts, wipers, door seals) before you drive it, because good chance the previous owner didn't do it and they are pretty worn by the time they sell it off. You wouldn't want a radiator hose to blow or a belt to snap when you're going down the freeway doing 75/80, that would be a pretty bad time!
Same with a vacuum, you don't want to do all this hard polishing work and all the time of taking it apart and cleaning rust off, and then have the motor die just a few months from now.
I try to get my vacuums to factory-fresh condition when I clean mine up, and replace anything that looks significantly worn. The carbon brushes get replaced along with the armature getting polished to remove carbon buildup. It helps get the motor's torque back and make the motor perform a little stronger, especially if the vacuum was severely abused. Running a worn vacuum motor will further wear it and eventually irreparably damage it, if not burn it up.
I too have a Kirby G5 that's been in a worse state that I hope to get repaired this summer. It looks worse than it is, a lot of it is just dirt.
