Sounds like the shift forks inside the tranny are worn out.
That happens when the driver rests his hand on the stick while driving.
I found out the hard way, years ago on a Jeep.
First, drain the tranny into a clean container, like the wife's mixing bowl and check for brass. (could lead to divorce though).
Pop the tranny top and inspect the forks and anything else you can see with a good flashlight.
Run a retractable magnet up the drain and down thru the removed top to see what metal shavings may be in there.
That will give you an idea about the condition of the tranny.
Then post what you find.
Don
