I have an older (1951) rolleiflex with the less sought after schneider xener lens. Although I think this is a great lens. Anyhow this camera was in rough shape I replaced the mirror and leather but the viewing lens shows some fog . Can this be replaced? it looks like it is sealed and can not be seperated to be cleaned also focusing is a bit dim I would like to put a frensel screen under the ground glass except the parrlex gizmo seems to be in the way . Anyway around this?