This WAS a rubber stick on cushion. These are often found as feet on electronic equipment. I actually don’t know why it was ever in there.
It didn’t stop there and ran all the way down the chassis. The first sign of trouble was that I went to pull the scope out of its housing and it just stayed stuck, but then came out with a big SCHLORP sound.
I’ve begun ripping these rubber cushions off my older electronic gear and replacing them with sticky back felt feet if necessary. I wonder if there are silicone rubber equivalents? The silicone rubber keypad on this oscilloscope still works fine despite being made in the early 1990s but that superfluous cushion had to go before. I’m glad I got it before it oozed right out the holes in the back.
As nasty as this would be I’d rather soak in that substance than the contents of the Tesla Dumpster Pool