Five little words..
Well, I went, I got quite muddy, I almost got flattened by a big dump truck thing, and I eventually saw the bird. I think the OS need to do a little updating - only one pool marked for Black Hill Quarry, I reckon there's at least 5 there! I think some different instructions may help - Park in a car park [there's at least 4], get on the East Devon Way [marked with pictures of Foxgloves and purple arrows], follow it until you find yourself in a stand of pines overlooking quarry workings to your north, look in the SW corner for a little grassy island with a couple of bushes on it. Oh yeah, take a big scope.
Right, now I've finished venting...
The bird is all Mark says - no rings, intact flight feathers,
very alert. Its got quite a nice spot - sheltered, plenty of grazing, nice island to roost on, and plenty of Mallards and BHGulls for lookouts - I'm not surprised its staying put. If it was further east, would I have been the only one there?