Make sure you use white lithium grease. Also make sure everything is very clean before applying the grease so there isn't any residual gunk that can compromise the nut.

I basically had the same problem. I got rid of the game before I could tell if the problem would reoccur.

I heard the replacement X/Y nuts had a run made from the wrong material. Could explain why some of them shred so quickly after being replaced.

That's probably it. I quickly ran through two of them no matter what I did. Finally had to take the game off location.