Does the gearstick go into the reverse position, but nothing happen?
Reverse has it's own selector fork which you can replace without stripping the box down. I busted the reverse gear on the original catflap and had to strip the whole box right down to replace the gear and shaft, which sits right in the bottom of the gearbox case. I had to buy a reverse gear 'kit' to replace the old one - I think there may have been a problem with earlier reverse gears and Land Rover improved the design.
Les.