[RobSC]

Here is what I have determined on my limited research.  The ISX (EPA 2007) is the engine that may have the valve issues.  It is the pre-DEF engine with a dual overhead cam design.  The ISX15 (EPA 2010) was the next model that is a DEF engine.  It has a single overhead cam design.

The above coach #1450 has the ISX I believe.  Newell probably had some remaining in stock, and the owner elected to go with the pre-DEF engine.  It may be in my best interest to look at later 2012's or 2013's.

Rob