I had a huge seed of grain stuck int he middle of my R2 VF. i couldn't see it when shooting because my eyes were focussing somewhere completely different... so there actually was no problem to solve.
Notwithstanding I decided it had to be cleaned, took my Bessa apart, peeled back the rubber, found the screws and carefully opened the top. Blew out the seed, and blocked the red meter LED from shining out the fron of the fresnel window at the same time. Nice.
Unfortunately, along the way I saw what it was made of, fell out of love with the camera, and traded it for an M3.
So, if it ain't broke, it may be better not to fix it.
YMMV
very best regards,
Alex