Anthony, I can't see how posting your experiences with a particular dealer as defamation. I did see that you went back to the dealership. Did you talk with the service manager to get some kind of resolve? I take it that you didn't get any resolve, hence this thread. If you're still not satisfied with your delear, contact someone higher up.
Yeah, you can be sued for just about anything these days but I doubt that a delearship would take the time and money to sue an individual person for defamation. Oh, when that story gets out into the media, the dealer would be shooting themselves in the foot. Maybe Melissa could give you more insight for the technical aspect of it.