For those itching to know about 'WH'
You can normally check its 'reliability' (or not) on Teletext - look for the BA1502/3 as stated above between JFK and MAN.
I do suspect that its something to do with not getting near the usual 767 maint @ LHR, and also there never being a spare (unlike LHR).
Its kept on that route because (I think) its now the only 2 class LH 767...
NoD