Revisiting this old thread, and am willing to give the old stone another try.

Sperm oil, (get your minds out of the gutter already for crying out loud!)
Is no longer available in the states. (and almost anywhere else for that matter) but was commonly used as the highest quality lubricant for watch making.

I will ask my watch repairing buddy, what the modern replacement oil is, and try to acquire some. Perhaps this is one of those stones that can change characters just with a tiny change in lubrication.

For anybody still reading, I will let you know!