John, First, the EGR cooler leaks would should up long before enough coolant form in the Plenum, We are Talking PPM 1 ppm = 0.00016035860569078 oz , Their 10,000s OA done on Eco's literally 100s posted and NO sign of internal leaking. Yes I have talk to many that did OA trends prior to the Fire that burned up their ED, If memory serve Me correctly BoBcat93 had a history of OAs and NO sign of leaking., In order for the soot to get laden with coolant it would take time to absorb it, or if it was all at once the engine performance would suffer.... NONE of the on road fires drivers have claimed lack of performance prior to fire.
John their are likely to be leaky EGR I agree with you on that but its not causing 100% of the fires Like I mentioned maybe 2-3% at Best.