That's a very detailed link. It does confirm my suspicion that the two screws hold some mechanism inside. Unfortunately, "In order to clean the viewfinder, it will be possible to lift the leather of the camera and force the case, which is not worth it in this case" is not very helpful. I had already thought to remove the leather over the housing, but this still doesn't look like it provides access. I'm increasingly convinced that the viewfinder is installed thru the front of the housing.
I don't often avail myself of Google Translate, but this is a great example of just how bad computers are at translating and the unintended consequences this could cause. Among the various obscure bits on that page that you can potentially struggle thru lies this gem:
"Apart from this technical refinement, difficult to find in other cameras (from the same time or later), the rest of the Virtus equipment is not turkey mucus."
Image the dangers of Google Translate rendering "Can you direct me to the station?" as "Please fondle my bum.".