Basically, all that makes a powerhead is an electric motor, a plastic impeller, and rubber seals. Motors usually dont "wear out" but if a motor seal is bad, the motor could be getting rusted. The impeller could be dirty or be broken and a seal could be bad and you are loosing intake or output pressure somewhere.
it is usually very easy to pull the impeller and inspect that and the seals. If they look good then it could be the motor. otherwise could just use some cleaning.