Looking for a source of leaks

Looking for the source of light leaks in the Zenit B. I think it's possibly coming from the area where the red arrow is in the image. There's a hole which was probably in the sibling machine the Zenit E light meter was attached. To the left there is also some signs of corrosion. So possibly linked. I can see a speck of light coming from this side in the view finder. I'll put some material in there and add some foam to the front of the mirror plate which is just a sliver of hardened material. It's that strip of material to the left of the red arrow. I suppose that was once rubber?
I could just through this away and get another Zenit body. But then that's a waste of material and money. I could also use this body to explore inside what is wrong with it further. The repair manual which I obtained from the Zenit users group has a list of options that are the common cause of leaks for this camera. The timer is jammed solid but I don't use that function mainly. Though that corrosion could've spread if that is what caused it.