ColColt
Established
This is what the manual shows the patch to look like. Mine looks nothing like this...it's close to invisible. More annoying is the vertical alignment is a bit out.
ScreenHunter_01 May. 25 18.23 by David Fincher, on Flickr

I have been using several Nikon RF cameras for decades and all in all I have had to adjust their rangefinders four times.That sounds awfully sensitive. How these were used in a combat zone seems a mystery. It was mailed via UPS but packed to the hilt with paper and peanuts.
Your S2 has more than likely a dirty RF half-mirror. The diagonal rear surface of the half-mirror gets dirty on almost all the Nikon rangefinders due to some grease outgassing from the lens mount helical, the winding geartrain and the shutter speeds cams, all of those being very close to the RF half-mirror. Like explained above, the diagonal surface of the RF half-mirror is trapped inside a metal casting. That helps the critical optical surface to get dirty.I suppose one question to myself is how, if that be the case, did the patch become faded or faint. I have some Leica M cameras that are just as old and they have about a perfect a patch as it gets.
If that's the S2 you bought, it is the envy of all the other S2 Nikons in RFF. Cosmetically it is a treat. If you want to let it go, let me know. If the curtains & film compartment match the exterior, it's a gem. --alfredian
Still we can have no idea of how your patch is since you seem to expect the same thing as what you see in your Leica M finders.My one gripe mostly was the patch.