havent ever torn a rover VC apart but I have a number of the jeeps VC and they are rusted!!
you wouldent think that rust could be a issue inside a sealed VC but I saw it with my own eyes more then once. the jeep boxes demis would almost always be the same...the VC would lock up and driving the thing causes the chain to break.
I think environment must have alot to do with it. sealed parts are not always sealed when they go through huge temp swings, and if the fluid in the main part of the box is contaminated then you have potential for corosion.