Fixing a Magnetic Tumbler

I own a Raytech, and need to fix it. The machine is about 5 years old. The shot is fresh, I'm wondering if the magnets are loosing their polarity. The shot spins, but not nearly as it did a few years ago (even one year ago). I was told it could be the brushes, however when I took the machine apart I didn't see brushes. I'm assuming they are the carbon rods that transmit electricity to the copper centre (?). I have new brushes ordered, but I'm not convinced that's the issue. The copper seems to be fairly worn out.

Advice anyone?

Thanks!