Photography - Rear cover foam in an old SLR

Replace the foam if you can. You can buy thin 1mm strips from
www.micro-tools.com

I picked up a circa 1978 Ricoh SLR from Good Will. I checked all the
mechanical motions before buying and they worked good, but upon closer
inspection after getting home, I discovered the mirror rest foam have
turned into black goo. I cleaned off the old foam with solvent and a
piece of rubber foam I got from a local camera shop.

I thought all is well, but I found more gooey black molten rubber foam
in the rear cover. I could replace the foam on the sides without much
pain, but the foam in the top and bottom grooves are only a millimeter
thick or so and I'm not sure how to source the part or fix it.

Do I absolutely have to replace the foam at the rear cover?