If you're describing the foam breaking down into goo?

Then you need to replace the foam. It ought not be goo. The shutter bumper is what the mirror hits when it pops up, and if that's not a soft piece of foam that you can touch with your bare finger, you seriously need to get it removed, cleaned, and replaced.

The foam does break down over many years from what I understand. It also becomes a big mess, and you don't want to get it anywhere such as the shutter, or on the mirror, or inside the optics or anything like that.

Some folks have suggested not taking this on yourself unless you know what you're doing. Others say you can get re-foaming kits online and do it on the cheap.

Regardless, if your bumper foam is rubbery, check the light seals around the doors as well. They may be going also.