Did the vet fully examine Rebel's mouth and teeth? I ask b/c a year ago Finn had some bleeding from his mouth too and it turned out to be a broken tooth which abscessed. At first the vet asked me if Finn got into some rat poison somewhere since that can cause bleeding. Then she took a closer look and discovered the tooth issue. She ended up extracting the tooth and Finn was fine afterwards. I know what the vet said is very scary but try to not freak out as it could be something as "minor" as a broken tooth. You haven't noticed any other areas of bleeding? Thinking if it's a blood clot disorder then he would be showing signs of bleeding/bruising elsewhere in his body too.