Is it on a stand or side mounted to the cage?
Either way, I would take it out of the cage and give it a good cleaning. Once you loosen the center bolt and take it off of the stand or the side mount you can make sure there is nothing caught in side the bearing. The spacer that fits on the bolt might just have an accumulation of glider pee or even bits of food on it causing it to resist movement.
If a good cleaning does not fix it you can contact Anita at Atticworx and ask for her suggestions on fixing it.
Their Email is: atticworx@bellsouth.net