Broken Slides
I hope this will help. The Majority of Slides used in any mast are Nylon except for the head slide(Usually). Nylon is of course prone to eventual UV Degradation, but they should last a long time.The Mainsail Luff slides or slugs, are guides and are not designed or intended to really handle the full sail load, that is the job of your halyard, and the Luff Rope in the sail. The most common fault of slide failure, is not enough Halyard tension. If you see "Scallops" in your luff, it means that you are point-loading your slides. When this occurs, your slides are taking all the load of your sail, instead of the halyard.When sailing, as wind pressure increases, it may be necessary to adjust your halyard tension to avoid loading the slides.This is also common when reefing, adequate halyard tension is not applied, and the slides are taking all the load. Now, couple that with the increased shock load of a tack or Jibe, and those little slides are going to have a tough time staying in one piece.Most Sailmakers should have a pretty good stock of different style slides or slugs that will work even if they aren't exactly the same kind as you had. But they may not have the plastic shackles. The reason sailmakers use webbing to attach the slides is because the webbing will articulate better than a shackle and it tends to distribute load better than a single point like a shackle.