I guess the question becomes how soon do you do maintenance before it is really before it's necessary. For example, my car's brakes will eventually need to be serviced. Like most people, I wait until there are signs that it's time. I don't do maintenance now to avoid a potentially longer time in the shop down the road. This is even more true when I know that I'll be trading or selling that car soon. Same goes for park rides I guess. Disney isn't inclined to take rides down to do maintenance before they have to and they will avoid maintenance on rides that are scheduled for a major revamp or retirement.