Hi Ian,
You checked your centre diff mount mate? if you can move the diff nose by hand then all you may need is a new mount.
I had a garage replace oil seal on diff pinion...fooked it up so bad had to put new crush washer on and redo the preload...bit if a pugs ear as you only get one shot with the crush washer/collapsable spacer then you have to take it to bits and replace again!