I can't prove anything is true which is why they are rumors BUT the reason these rumors persist is because of his past behavior. Notice how no one ever has accused Mike Pence of anything like this. This is the guy who cheated on every wife including fucking a whore on his desk while his wife was recovering in the hospital from giving birth to his kid. He also bragged about "grabbing them by the pussy." The list goes on and on.
No, the rumors persist because the left is desperate to keep this in the mainstream and in the voter's heads. You yourself posted the comment about the 12 year old which wasn't true, or at least you couldn't provide any link to it.
If evidence existed on this, it would have been brought to light long ago.
And all that stuff you listed - cheating, whores, locker room talk, is NOTHING compared to kid stuff, and there's no evidence of any of that.