Pinball machines are kind of like used cars. As time goes by, they get used and their condition deteriorates. Therefore, they require reconditioning to regain value. There are exceptions to this rule, but all pinball machines require service whether they are played often or not. Batteries go dead and leak, capacitors lose their efficiency, display tubes become dim and things just wear out.
Pinball machines were designed and manufactured with one thing in mind; profitability while in operation. Their life span was expected to be between 3 and 10 years when on location in the arcades, with regular maintenance. With that in mind, what kind of condition is your machine in?