The issue is you would need heavy industry to actually be self sufficient, systems essential for life would inevitably break down and it takes that to fix them. Radiation and impact events would damage the hull over time, solar panels or reactors would need repairs, and moving parts or communications equipment would break. Even the simple act of maintaining an atmosphere would degrade the ship over time. You would probably want engines or thrusters to keep a stable orbit, or in case a big asteroid came close to intercepting, and that would definitely require maintenance.