A-883

The detent spring/ball assembly has two hex parts, if you loosen the outer hex plug you can take out the spring and ball with a magnetic pen or something.
Then you can take out the other piece of the assembly and put on a new gasket.
Slide the ball and spring in place, put a new gasket on the outer plug and screw it in. Finished.

Oh, and don't forget to drain the trans of it's oil

Antoon