The Nikon scanners do not require regular maintenance. They are however quite prone to dirt and dust. Your best bet keeping the scanner running problem free for a long time is to store it in a clean place (wrapped in a cover) when not in use. Some units are also starting to show signs of age and may e.g. have problems with the lubrication drying out. They also have moving mechanical parts made out of plastic and these parts can wear out and break. The last problem is not so closely related to age, but how much you use the device.
A great problem with the units which are actually failing, is that Nikon for a long time has not provided service anymore for these scanners and there are usually no spare parts obtainable if something should fail. Even if the units are now some 15-20 years old, they retailed for several thousand dollars and one should perhaps expect more from a manufacturer like Nikon.