Oh no! I'm really, really, really sorry to hear this
I honestly don't know what to say. He was a great little ham and I'm really sorry he's gone. I hope Pepper can help provide some comfort and rest in peace wonderful little Salt
Also, just had another thought. I hate to say this but I'm scared of it so want to make a suggestion. If I were you I'd try and find another vet now. One who would know hamsters. I know you won't want to hear it but theres no guarantee it wasn't genetic or contagious and I really want to know there's a good vet ready to help Pepper if he ever needs it.
I'm sorry to mention that, but I felt you should be prepared just incase. Theres a very high chance Pepper is fine, but a good vet'll be needed eventually either way.
I know Salt is happy at the bridge now, pain free, no longer circling, happy and relaxed. Playing with all the hams who've gone before. I know Pompompoms Jam is always there to help new robo arrivals and so are hundreds of other wonderful HC hams. Salt will be happy there and one day he'll see his brother there again too.
Play well little Salt