VW Van Fuel Pump

I have a VW diesel Van (Camper Van) that I have rented in Australia. The company advertise that all of their units are within 3 years old - so I assume that it is no older than that. It has 76,700 Km on the clock so it is not a new vehicle. Because it is a rental - I have no idea of its previous history.

I inadvertently filled the tank with high octane unleaded fuel (the guage was reading 1/4 full when I filled the tank). I drove another 50 Km before the van stopped. I subsequently had it towed to a garage - the system pressurized and drained of the unleaded fuel and refilled with Diesel fuel. We have since driven an additional 1000+ Km and filled the tank another 5 times. After going this distance, it began to missfire - and stall, then within the next 500 yards the glowplug warning light came on blinking as we drove. I immediately turned off the road and stopped. The garage has preliminarily diagnosed a fuel injection pump as the problem and the rental company is saying this is directly the result of the wrong fuel 5 tankfulls ago? Is this possible?