Problem with tranny

[titengo]

My car runs fine as long it is forward. When i put reverse it backs up but when i move the shifter it stays in reverse no matter in what position is the shifter. I dropped the tranny and found that in the gear selector assembly there should be something like a metal ball or something that there isn't (it has wear marks), but i went to mopar and checked the manuals but it's not there. Don't know where to go, any help would be appreciated.

 

[titengo]

Here are the pics. The first one shows where it should be, the second one is to show the wear marks, and the third one is the two pieces assembled.