There could be a chance that the valve that was sticking is not sealing against the seat and you still have a compression problem. Oh and that dealer that said they wouldn't honor the warranty because you didn't change the oil after the initial 5 hours is lying through his teeth. Unless they can prove that the oil went bad after 5 hours and caused your problems they can't deny it. He just didn't want to work on it. Low oil level they can cause warranty problems with. But you have a warranty problem, and a dealer needs to take care of it.