A little strange that this is so unrecognisable to others, esp as its only 3 or 4 miles from the Heritage Centre.
This Drybrook is the "Little Drybrook" near Ellwood Lodge; just north west of Bream, towards Marsh Lane and Clements End. Take the road from Bream Tump out towards Sling, around the Mill Hill bends, half way to Sling - then head north into the Forest and you'll find the small settlement..
OS map ref SO 595,072
< use Google Maps, and place name Little Drybrook, for road map and satellite image >
The Walks and Inclosures were divisions of the Forest.