Why not just space the gray after you get underway?
I always figured if any of the Greys were found intact, but inert, aka “dead”, there would be some Booby Trap device implanted. As soon as our earth scientists began tinkering with, or opening up a non functioning Grey, for an ‘autopsy’, there would be some poison gas hissing out, intended to sicken and kill that earth scientist before he could even say “Boo!” Okay. Maybe I’ve been reading too many Adventure novels.