Worn? Really!? If they were "worn" out the shells would come out of the tube on their own as in one example above. Remove the stop arms and make sure the slots in the receiver are clean. They need to be fully recessed into the frame when fully cycled for a shell to come out. Are you pulling the slide all the way back? Shells ejecting!? Did you bend the stop arms or lift platform by hand for any reason?
Also, is the magazine follower sticking!? Lube working parts with a very little silicon spray.