The one-way bearing in both plastic and aluminum autorotation hubs has been known to become loose. Usually when this happens, the one-way bearing can be pushed out of the hub with firm finger pressure.
This can be easily fixed by roughing up the bearing and autorotation hub mating surfaces with 200 grit sandpaper and using thick CA to reassemble the unit.
The tail blade grips (67542) should be checked periodically to make sure they are not too loose. If they are, be sure to unscrew them from the tail rotor hub and apply fresh loctite to the screw before reassembling.
The main rotor shaft bolt (67599) is rather soft and can become bent in a hard crash. Be sure to check this bolt if the main rotor blades have hit anything. If the bolt is bent, be sure to replace it and do not fly with it.
The battery holder O-rings (67587) will need to be replaced about once a year because they will start to crack. These can be replaced with the stock Ikarus parts or you may be able to find the O-rings(30mm ID x 3mm thick) cheaper elsewhere.