I admittedly do not know much about these VW common rail engines. However on a VW Facebook group there is this theory going around that your exhaust should be spotless and if it isn't and there is any soot you have a cracked dpf. I understand the logic to a point but isn't that almost impossible? Seems like some soot/dirt debris etc is going to get in there. Anyway wanted your thoughts my car is a mk6 Jetta but this is apparently true for all dpf systems I took a picture of my exhaust and the "spot".