I have a SA 7 and SA 9 both have penta prisms that are yellowing. I have a couple of SD 9s one of which the AF is no longer working but the penta prism is still clear. The SD 9 is built on the SA 9 body, so I am thinking that I swap out penta prisms. First challenge is removing the shutter speed and mode dials. I don't see any set screws. Any thoughts on how or proceed? Friction screwdriver?