Check the linkage, unfortunately you'll have to lift up the floor panels etc to get a good view.
If the landy has been used off road, and the hi-lo has been used ham-fisted, there is a part of the linkage that's made to *give*, it's one of the jaw ends and it's made up of a pressed steel affair.
This is the part, it folds up if the linkage is abused, so you finish up loosing either high range or low range.
Where it's fastened to the bar with 2 nuts, you can adjust the length of the linkage, this will then *adjust* where the gear stick moves, so if it's hitting the side of the opening in the top of the tunnel, you need to adjust the length so that it doesn't.
Where the pin goes through to connect it to the lever, there are small plastic bushes in the jaw end, these wear/ fall out etc, and are a pain to get in (I stuck mine in with a dab of superglue to hold them in whilst trying to get the jaw end over the lever.