904 Transmission Stopped Going Into Gear

Every single time a trans needs the throttle played with for the car to move it needs a rebuild.
(Sometimes) a full bottle of stop leak or "conditioner" can make the seals softer and they work for awhile, but it's a total temporary fix.

I have NEVER seen one come back from that by adjusting or changing any part except a really plugged up filter, and if the filter gets that plugged up it's coming apart inside anyway.

Sorry for the bad news, but that's just the way it is.