If you are unable to get the projector to function in reverse and you have moved the adjustment plate to it’s full travel, you may have a gummed up “Directional Lever Assembly”. When the reverse button is held in, the solenoid should be energized making the “Directional Lever Assembly” pivot. No pivot, no reverse, not pivoting fully, no reverse. I have attached 2 images of this area/lever. One with the mech in the projector so that you can see where it is and one with the mech outside of the projector so that I can show you the points better.
The bearing can get gummed up as well as where the lever rides against the plate. You can test the levers action with the projector turned off. Press the tip of the lever down (the end closest to the lamp) and it should pop right back up. If it does not move up and down freely, it needs cleaned at the points indicated with the pink arrows.
To clean this area, we use a spray degreaser that is safe on plastics.
Another issue could be that there are remnats of broken platic parts floating around inside the projector jamming it up. You might have to losten up the screws holing the mech in place to shake or blow out stuck plastic remnants. Lostening the screws normally is enoung and shouldn't require the removal of the mech.