Well. It's a gorgeous evening, so I popped out to Buckie and have just enjoyed a guided tour of the Mill of Buckie, Parish of Rathven, courtesy of the owner, who was very interested and most helpful.
There were two mills at Mill of Buckie, both worked by a lade that was fed by the burn that comes down the west side of the Inchgower Distillery.
The first one was a meal mill, with two wheels. It was mostly built of wood, and had become riddled with dry rot, so it was demolished and the wheels were sold to a mill preservation society and are probably still in use somewhere.
The second one was a threshing mill, and it is still standing, though no longer in use as a mill. I saw the lade coming in at the top, and a steep drop to the Burn of Buckie below the mill. The shape of the wheel is still discernible on the outer wall, and it must have been a very large wheel - we reckoned about 15 feet in diameter.
It was all but impossible to photograph because trees have grown up very close to it, but I had a go, and I'll put the photos on the Geograph web site in due course.
I still wouldn't dismiss the possibility that it's the one in Glenbervie, or even another similarly named mill.