Guess on the cause of these symptoms?

comment number 10 is the key here, but he didnt go far enough to explain. It is the brass STOP ring which stops the freewheeling gear enough to slide the slider ring onto the gear. If it doesnt slow down enough to 'synchronize', the slider wont engage, and you hear the grinding. So the underside of the ring does the stopping, and you can not seethat condition installed. Lets assume the builder didnt go cheap and not replace that, even if the top looked 'good'.