When I got mine the difflock lever was very stiff! It went in to high and low which is back and forwards but not to the left which is diff lock, I stood outside of the disco on the passenger side and pulled it hard towards me and wiggled it and it eventually moved, the light didn't come on so i assumed it was a bulb out but I put it into difflock the other day and the light came on!
Have a go at that but be careful as if it's really stiff it may bend the selector rod thingy.
Cheers Matt