What hint is there that he may be of use to the Squire and his friends?

Ben was with Flint when the treasure was buried.

"Now, I'll tell you what," he went on. "So much I'll tell you, and no more. I were in Flint's ship when he buried the treasure; he and six along--six strong seamen. They was ashore nigh on a week, and us standing off and on in the old WALRUS. One fine day up went the signal, and here come Flint by himself in a little boat, and his head done up in a blue scarf. The sun was getting up, and mortal white he looked about the cutwater. But, there he was, you mind, and the six all dead--dead and buried. How he done it, not a man aboard us could make out. It was battle, murder, and sudden death, leastways--him against six. Billy Bones was the mate; Long John, he was quartermaster; and they asked him where the treasure was. 'Ah,' says he, 'you can go ashore, if you like, and stay,' he says; 'but as for the ship, she'll beat up for more, by thunder!' That's what he said.