I noticed that Minky has a black dot on the back of his ear. You can't see it from the front, only from behind. It looks like a blood blister. It's very dark.
I haven't taken her to the vet yet, I've had too many rats "using" my money but if it gets bigger I will. Let me know what you decide? I personally didn't think it was serious.
I've checked Jani's dot and it doesn't seem to hurt her and it seems to stay on just the one side of the ear like it doesn't go through the ear. I would simply keep an eye on it.