Freewheeling hubs have been set to free for months, ever since the diff started to play up.
I'm barking up the wrong tree anyway, the vibration will be the transfer box, propshaft/UJs, or rear diff so this thread is a bit redundant. There is play in the outpust shaft so I may be looking at a new box, this is on top of the leak.
Need to have it up on stands again tomorrow for more maintainance (wheel cylinder) so I'll take a look at the UJs tomorrow.
Its just vitally important to keep it on the road right now with the Disco dead, we simply cannot afford to be car-less. If its Ujs then I'll get brand new bits as I'm building up a shopping list already :)