diff leak

ive noticed my rear diff has a bad leak,it seems to be coming from the end nearest the flange so im assuming its a seal thats gone..is it an easy job to replace the seal or is it cheaper and easier to buy a 2nd hand diff,,i have to remove the props at some point as i have new heavy duty ujs to go on and i have to replace the front diff as its whining like a bugger..

The seal is easy to change.
Drop the prop, undo the big nut in the middle of the flange, pull out the flange and spacer, lever out the old seal, knock in a new one with a 52mm socket.
Re-fitting is the reverse etc....

Have a look in the series gallery some most excellent bloke put an article in there a while back