I would not use any metal tools to scrape out the old foam seals. Get a bamboo chopstick from a Chinese restaurant and trim it down to fit in the grooves. Then you won't scratch the metal camera.
The prism rot is common but won't affect the photos. When you clean the camera, find the web site that shows how to remove the top plate and get that old foam out of there. You have to be real careful since there are delicate things in there and you don't want to drop any of the foam crumbs into the viewfinder.
Don't destroy the film advance lever's cap screw. Use a rubber sink stopper as a friction tool to unscrew that thing.