Broken transfer box ?

My faithful old Disco ground to a halt in Wales at the weekend. The problem appears to be in the transfer box (selecting any gear and releasing the clutch causes a sound of gears or gear dogs trying to engage). The 'high / low' ratio gearstick seems to be doing very little when moved back and forwards (i.e. from low to high ratio). There is no sensation or sound of teeth engaging as the stick is moved, just a steady and small amount of resistance across its travel. The linkages into the top of the transfer box are all in place and moving as they should. My suspicion is that the shaft that moves the selector fork in the transfer box is not being moved by the lever and the gears have moved into the neutral position (albeit up one end of the neutral position - hence the grinding noise) and hence no drive to the propshafts and beyond. Has anyone else heard of this problem before please ? Also, does anyone know whether it's possible to remove the section of the casing on the top of the transfer box (so that the fork that moves the selector shaft can be viewed) without first having to drop the gearbox and transfer box out ? The car is currently 250 miles away and so I'm gathering tools and my thoughts before heading off to fix it. Any words of wisdom gratefully received.