Fails to advance the cloth

Question

I know almost nothing about seweing but bought this machine at an auction. It is in beautiful shape with many accessories, but it seems like the two feet that should advance the material have almost no teeth on them. They function correctly, but seem to be worn off to the point of not ''grabbing'' the cloth. What are these called and are replacement ones available? Is this a common item to wear out or am I just not doing something correctly? Thanks for any help you can give me.