What determines buying a new garage door opener?

Answer 1

If you need one and it cost more to fix the old one than it's worth. Judgement call. A new one is around $150. Anything over $80 in repair would justify a new one. Having installed hundreds, Sears 1/2 horse chain drive or Chamberlain, it's the same thing has the least issues. A properly balanced door need very little to open and close it.