Hey, for what it’s worth, the flea possibility you mentioned would be good to rule out. I’ve seen cats who absolutely mutilate themselves over a single flea. And internal parasites as well, given he goes outdoors, hunts (?), I assume occasionally eats something gross in his explorations, and if he has ingested a flea could have picked up tapeworm…
Has Ralf been dewormed recently and checked for fleas? I’m just wondering if he brought something “home” with him (It’s wonderful he came to live with you!)