Detent ball fell

Drill a hole in the bottom ;^) ( not helpful but hopefully it made you smile.)

You could try a magnet on an articulating arm and get lucky.
Just a wild thought. get a long skinny spring like from a screen door and run a small cord down the center. tie a small doughnut shaped magnet to the cord and pull snug to the spring. the harder you pull the string the spring should arch. you might be able to get the spring to the low point of the trans and pull the ball out. Probably quicker to pull the trans.