As far as I can tell (and this is speculation) the cars that have burned thus far are all left hand drive. I'm trying to establish exactly what is being vented through the breather pipe but don't have an answer as yet. Could it be as simple as a build up of fumes venting through this area being ignited by a driver casually throwing a still burning cigarette end out the window? That would tie in with the affected cars being left hand drive. I had one of my 18 wheelers set on fire by a carelessly tossed cigarette by the driver on a motorway. The still burning butt end got sucked into the air intake system in one of those million to one chance events and started a catastrophic fire. The fact that none appear to have caught fire on tracks - where there is a much greater risk of mechanical heat build up - also makes me wonder if the cigarette theory is more than pure conjecture on my part.