I have a 99 XC with about 140,000 miles. I have been meaning to change the angle gear oil for probably over a year. Kept deferring it. The car developed a whining sound when the car was cold that I thought was from the angle gear. Even after topping the angle gear oil off, it still whined.

I changed the oil with the expensive oil sold by the dealer. (About 35 bucks for a liter of synthetic gear oil.) It made a remarkable difference with the whining sound that we had. It is for all intents and purposes gone now.