How often should you change out the o-rings or is this a common sign that they are getting worn?
I can't answer that. I have not seen any suggestions or stats on how long they last nor anyone saying this is what happens when they are worn out. I am confident though that as they wear or get soft blade tracking could be a symptom. Have you lubed the O rings well with dielectric grease? If they cannot turn freely on the feathering shaft you will have various issues.