I bought a RB67 ProS that came with a 127mm C lens. I found that the lens had fungus and haze around the next to last lens element. I took it to the shop for cleaning but was told after the lens was taken out that the haze was because the lens group was seperating due to bad storage. The haze is only around the outside edge about 1/4". What effect if any will this have on the image and should I think about replacing the lens with another. I would like to see if I could find someone who has a broken lens that would sell me the lens group so I can repair this one, the rest of the lens is in really good condition. I haven't shot any film yet, I have to replace the seals in the back. Would you keep it or replace it?
127's and 90's are really inexpensive, I'd say replace it.
The haze won't affect sharpness but will flare a bit more easily. A lens hood will help if you don't have a backlit subject.
There is another possable cause which looks like separation... edge blackening is worn or washed off. It looks like separation whn loking through the lens, although in 40 years I have never seen separation in Mamiya RB lenses, your repairmen may have over looked this very common problem.
There are 2 varieties of 127Cs. One the front cell screws off like a light bulb and the second flavor, the name ring has to come off then the front cell unscrews out like a bulb. If you can see the sides of teh cell, you will notice by holding it to a light, the blackening scratched or worn anywhere along the edges. If so, flat blackening repaint is the cure.