@ Timotao
That camera is not a diamond ring and at this point it sounds reasonable to go on with the service you've begun to perform. You were smart enough to remove the front plate and the focusing helical without damaging anything. I see that you put the screws that hold the focusing helical back onto the camera chassis not to mess with the shims which are underneath those screws, so my guess is that you have the skills to go on and fix your problem.
🙂
Could be that debris of some sort is locking the swinging optical unit of the rangefinder, or that something is blocking the light within the rangefinder path. In my opinion your camera isn't broken. I have several Nikon RF bodies, some were in shoulder bags which were unintentionally dropped from my body height and they got the bumps. Worse case, their rangefinders were in need of vertical adjustment afterwards, but nothing got broken ever. A more severe shock would have left some very visible marks on the camera cosmetics and the lens optics would have been blown away too! The Nikon rangefinder cameras are robust machines.
I am thinking of the flash sync. yellow wire you will discover under the top plate being desoldered at one end and now laying in the rangefinder optical path. This is common, happened to me once. Could be something else but this is very probably a begining fix.
So, now you need to remove the top plate. This is not difficult if you are very patient and very careful with 1) the flash sync. post, and 2) the A/R knob, not to damage them while taking them off.
Here you go (you can go on looking at Richard Haw's sketches, of course) :
https://www.nicovandijk.net/nikonS2repair.htm
Once the top plate removed, you will check that nothing is masking the rangefinder optical path and that you can see the rangefinder unit mobile parts move when you gently actuate the rangefinder pulley back and forth with your finger.
Caution : NEVER EVER touch the three set screws that hold the rangefinder prism located behind the small window of the front plate, NEVER EVER remove that part or you will never be able to reassemble it properly.
Best of luck, keep us posted.
🙂