Here is a photo made with my first couple Fed S + 2/50mm. The lens was (and is always) in a "misty" condition. And the patch of the rangefinder is invisible.
Probably I already showed it. I look for other ones, more recent.
Yes, that would be possible to clean when dismounting it by the front. You have a direct access to the diaphragm. So, cleaning directly four surfaces is possible. Perhaps it would be enough for you? Probably not for me: I think that the cemented surfaces are affected.
I have not tried anything on this particular 2/50cm. I have other ones which are in a good condition. This Fed S and its lens were my first purchases in Feds, 15 years ago...