Jenn,

look at it this way.......the chances are remote. It wasn't as though every DD was blowing up so already the odds are in your favor. The one you are looking at has some experience behind it so I would say that improves the chances the engine is perfectly fine (assuming the codes are checked by DD). Is there a risk? Yes. Is it a meaningful risk? Probably not. Can you predict it? No.

When this type of catastrophic failure occurs the problem is internal and mechanical and there does not appear to have been any way to predict which engine had the problem or when it was going to happen. The worst thing that can happen is you end up with a bus with a new engine you paid for out of your own pocket. The best (which is most likely) is you own a coach that will prove trouble free and reliable with 140K miles of its life used up.