What is happening to the rangefinder patch of my Leica M5?

Hello,

I'm here with probably a stupid question, but what exactly is going on with the rangefinder patch of my Leica M5?

The condition got worse after I used it rather extensively for a few days in <5°C weather; is this the "famous" balsam separation?
Out of curiosity; what part of the assembly is separating in this case, is it the achromat?
I can't see anything out of the ordinary when I look through the viewfinder from the front (even with a strong light shining through it), so I'm guessing the problem isn't with the beam splitter?
The structure outside of the patch in the attached picture is the paint on the wall, not something happening in the viewfinder.

Thanks in advance,
Alex

It looks like separation to me and it could well be affected by temperature as materials expands and contracts with temp variations.
I notice the degradation follows the edges of the RF patch so I don't think it can be the achromat - it covers a larger area. I would guess it is something glued that has the exact shape of the patch.
Exactly which component is beyond my paygrade.