I believe the Fichts are using the same Fastrak mid-section their earlier motors did. What I would do is take a large screwdriver with a large flat blade and would rap on the back of it with a large hammer while the blade is set into the slotted head. What you are trying to do is to "unfreeze" the threads by puting some inwards pressure on them. Then try putting some vice grips on the shaft of the screwdriver and lean into the handle with all your body weight while you try to back off the screw, which should come out about 2 turns to release the motor. You may need to hit the head of the valve body with a "heat hammer" ... meaning a torch. Take all precautions necessary if that is the case.
If needed, there is an "Internal Cir-clip" (like above - bottom right) holding the manual release valve from backing all the way out. If you need to remove it to service the valve body, it will need to be removed using the special pliers, as they make these for Internal and External cir-clips.
Please NOTE that you should tilt the OB all the way up onto the towing or mooring rest BEFORE doing so. And ALWAYS make sure the OB is secure before pulling that valve or the reservoir cap ... as you don't want to jam/lose a body part!
Note that once that valve is removed, you will lose a lot of fluid and if so, the OB cannot be tilted up manually (even with valve backed off or completely out) due to too much air being inside the system. Once you remove the valve, take a good look at the O-Rings. New valve bodies are $45+, so be careful with it, but you usually don't need to do anything other than clean it and lube the threads with OMC/Bomb "Triple Guard" grease ... get some and use it on all zirk fittings on that puppy, plus on prop splines.
To refill the trim/tilt unit, keep the OB all the way or part way up and locked into one of the OB's tilt lock positions
(trailering or mooring position). Put the valve back in tight and have a friend handy. Un-do the trim reservoir cap and insert the trim fluid tube; I use a small long/slender nozzle to help keep it in there. Have your friend press the UP button as you put in ALL the fluid it will take. Keep pressing UP while the OB goes all the way up and
you hear the t/t motor hit the bypass valve (motor sound will change) and
until the t/t reservoir won't take any more fluid and it starts to back out. Mind you, your friend's finger is still on the UP button ... and while doing so with the UP button, quickly put the reservoir cap back on.
The concept behind holding the UP button allows the motor to suck in all the fluid it can while attempting to push the OB all the way up. Doing in this way you should not have to top off the reservoir again. But to check - remove the locks and cycle it down by jogging it down, 2-3 seconds runs. Then rest the motor a few seconds, then go UP all the way. Rest/pause again ... then repeat that cycle 3+ times to ensure it has bled out all the air in the system, if any ... as these systems are self-purging of any trapped air.
Good luck, hopefully this will help. Post back if you have any issues or didn't understand something.