I recently purchased a couple of old maps of Bodmin Moor, one is a military map from 1946 the other is from 1961. Both mark a fogou on at this grid ref just north of Brown Willy. It is still marked on Os maps as late as 1970 but is not on the modern Explorer.
This is one area of the moor I am not too familiar with and it is also an area best not ventured into in deepest winter.
I will keep you all posted if I find out anything.