When you depress the button on the top of the shifter you are moving a
rod downward. There is a foot on the bottom or the rod that engages the
sector mounted to the shifter frame inside the shifter box. The spring
on the push button holds the button up and holds the foot in contact
with the steps of the sector. If the foot breaks or comes adrift of the
sector there will be no other indication of gear position other than the
steps on the similar sector inside the transmission that requires no
action but the movement of the shift rod to command a gear shift,
neutral or park.

Additionally there are nylon bushings at either end of the shift rod
that wear and fall out. when this happens the shifter becomes very
sloppy.

Bob