A rotary dial should last for 50 years or more. If yours seems to be slowing down or dialing wrong numbers, or both, you can rejuvenate it.
Remove the telephone shell. Loosen the two screws that hold the dial in place. Turn the dial over. Remove the plastic dust cover if there is one. Put a blob of petroleum jelly on a toothpick and apply it to all of the gears. Spray contact cleaner on the contact points ("springs" in the diagram). Exercise the dial about five times.
Contact cleaner is available from RadioShack, home centers and online.
There have been many varieties of rotary dials. This diagram is typical.