I have one of these rakes (in different paint and double rotor configuration) and it has been absolutely abused in its past life. Welds everywhere. I have broken multiple arm shafts in the rotors which is way less fun than breaking external arms. I have, however, never broken what you’re breaking (have bent some arms but never in that location) and there’s no evidence among the rake’s battle scars that it has been an issue in the past. And that’s the long way of my saying this shouldn’t be normal or expected and there has to be (or had to be before you bought it) some abnormal wear or misuse causing this. If you’re absolutely sure there is nothing contacting anything anywhere (including making sure the stubs/inner arms for those particular arms aren’t bent down causing them to run into the ground when the rest are at appropriate height) then I would buy new arms and run it assuming the issue was something the previous owner set in motion. Also you should definitely check part numbers and compare prices, if you could find NOS vicon/kvernland (not too likely in the US but not impossible) that would probably be cheapest but outside of that Kubota painted arms are probably cheaper than NH arms.