All those symptoms you are describing sound so familiar yet i mentioned what it could be, it gets ignored. That pin actually mates the shifter link to the trans if there is something else other than the pin you have play, i.e. shifter moves around freely while in gear ( [ ] ) < example. The pin should be snug with the trans/linkage like so
(( )). Of course looking at it from an ariel perspective.
Just make sure you let us know what was wrong.