Ocean Mist,
DEF (Diesel Exhaust Fluid) was introduced in 2011 if I'm not mistaken.
I think you are talking about the DPF (Diesel Particulate Filter) which was required on the 2007 chassis's and later. We had it on our 2008 Monaco Dynasty.
Some manufacturers bought many pre '2007' engines to install their 2007 and 2008 coaches. I have even seen non DPF in 2009 coaches.
Calling the DMV might be your best bet for the most accurate information.
If you are required to add DEF system to an engine, it would be cost prohibitive I would imagine.
Good luck,
MM.
