it may not be the spring. remember that as the gears get higher, the parallelogram is collapsing. one piece is supposed to fit inside the other as it collapses. anything, a ridge, junk, a worn pin can cause the two pieces to hit one another and prevent them from nesting properly. as they age, a bur or ridge can be created on the large outside piece of the parallelogram. the fact that DR's use the small cog so rarely just amplifies the problem.