nitro kid - I would replace the rings, balls, and thrust bearing. Your kit should have come with instructions on how to properly rebuild it..and everything will be fine if you follow the directions word for word.
Derek - They are aimed at any track where Pro-Line would use Holeshots. You can use them on Taper-Pins style tracks, as they will often last longer than Tapers. Ideally, any moist clay, or outdoor tracks with a light layer of dust or loam.