BA/BN armor is not rubber, according to the old Leica ads, but polyurethane. Having owned a few, I'd say that compared to the alleged rubber on other binoculars I've owned, it is harder and tougher. It also utterly lacks the unpleasant odor of my supposedly rubber clad Ultravid BR.
I don't know what that white stuff is, but I seriously doubt it will damage the armor. However, reconciling the supposed polyurethane-ness of old Trinnie armor, bowling pins, and floor/furniture finish is beyond my ability. I guess it must can be morphed, plastic like, into different manifestations.
Despite my nerdy technical interjection, I appreciate ND's amused point of view about this cruddy looking binocular and its seller. White stuff has always been a great mystery. I cannot resist here telling a joke from grade school, which has always stuck with me, because it is, I'm sure you'll agree, both deep and widely applicable. It even has an ornithological overtone.
Q: What's that white stuff in bird poop?
A: Bird poop.
Ron