How can a worn rubber end of a composite rear spring be repaired on a 1994 Chevrolet Lumina?

The transverse rear springs start to grind over bumps when the insulators wear out. Go to your local parts supplier and get the two Teflon blocks, Moog makes this part. If the ends of the spring are still o/k not splitting you can pry (long bar or floor jack) the spring up off of the seat and slide in the blocks. You will see that the blocks have 2 raised sides, this is to hold the blocks in place once you put it in.