[Pilot2519j]

There must be some degree of culpability in this picture by the dealer otherwise the Porsche rep would not offer a new engine as good will. The fact that the story changed several times makes it very hard to believe any story coming out of the dealer. My recommendation since the Porsche rep seems to be so accommodating dig deeper using him. Consumer affair agencies and the likes will help to put some heat on the dealer and seek resolution of this matter. Or you can sue him for damages. Pick your poison in this scenario because it will not be either fast or pretty.
The other possibility would be to question the mechanic that worked on your car and see if he opens up or if anyone else will tell you what really happened. Or go to other Porsche mechanics in other dealerships and ask what are the possibilities of what happened to your car is factual and if there is any anecdotal data to back up the dealers story.