I feel pretty dumb at the moment. I can't seem to find the screw you are talking about. I tried to look at the manual you posted but I can't find any similar ring that can be the retainer. I don't want to do anything do destroy the shutter so I thought it best to ask for some more help. Here are some images from my shutter after I removed the front lens element:

bilde 1.JPG bilde 4.JPG

As you se in the photos. There doesn't seem to be a screw for the retainer ring