The solution depends on whether your shifters are '07-'08 escape models (Centaur and lower levels) or the traditional mechanism used for all other years and models.
There are only a few common problems with the later - broken g-spring or g-spring retainer. The indexing gear can also become worn, but usually only the right side suffers this problem, since it gets lot more use.
If the shifters are the escape model, I've got no clue. I avoided using those.