I changed the rear Dif oil on the terrano a few days ago. The difference it has made is huge. No more rumbling in reverse, seems smoother and the odd squeaky noise on the over run which I thought may have been in the clutch has gone as well. It was thick on disgustingly dirty and a lot of gooey build up around the drain plug. I think I will do it again in a few weeks time to make sure it is all flushed through. Really surprised at the difference it has made