Very sorry to hear about this. I had a case of panleuk in my house when I brought in two new kittens, unfortunately one passed and one luckily survived it. I kept my two adult cats away from them as soon as I found out about the panleuk and everything is fine now. This is a very difficult thing...
My cat Rocky was having rectal bleeding, he is 5 years old and I did a stool test at the vet. Everything turned out fine and he has no more bleeding, I think it was just constipation or something.