About liability...hmm...that's not the first concern I have in mind when I try to repair something. If the part is properly planned and manufactured I'm satisfied. I'm certainly not going to ask some authority if I'm allowed to do something. If I would the answer would most probably be "NO" because there's no one who wants to take any responsibility. As long as manufacturing or repairing some part isn't clearly prohibited I'll assume it's allowed. Asking unnecessary questions just leads to more and more prohibitions and that again kills the initiative and ingenuity.